Enhance any meal or holiday table with this easy Cheesy Broccoli Cauliflower Casserole. This Vegetable Au Gratin is ready for the oven in 15 minutes. Easily adjust to be low-carb, dairy-free and gluten-free.
As we enter the holiday season, easy side dishes are a must and slam-dunk recipes like this vegetable au gratin are always a winner. You will also love my broccoli gratin, potatoes au gratin and ultimate green bean casserole.
I enjoy giving precise details in my recipe posts to lead my readers through any questions. If you’re just here for the printable recipe, you can Jump to Recipe to head straight there!
Why You Will Love This Recipe
- Classic Holiday Side Dish – This Cheesy casserole is an easy side dish for a holiday meal, like Thanksgiving or Christmas dinner.
- Kid-Friendly – This crowd-pleasing dish will keep everyone returning for more, even the pickiest of eaters!
- Full of Flavor – This cheesy, creamy goodness is more than delicious! It’s pure comfort food, healthier than similar recipes, like potatoes au gratin, but has just as much flavor!
Simple Ingredients for Broccoli Cauliflower Casserole
- Broccoli and Cauliflower | Fresh cauliflower and fresh broccoli florets bring the dish a crisp and tender texture. Fresh is best!
- Oil | Use olive oil to saute the onions and garlic.
- Onion and garlic | Add flavor to the sauce with chopped onion and minced or pressed fresh garlic. Replace the garlic if desired, with garlic powder.
- Flour | Thicken the sauce with classic all-purpose flour, giving a base for all the delicious flavor. Gluten-free flour may also be used.
- Half and half | Make a creamy cheese sauce with half and half.
- Cheese | Melt down a combination of shredded Swiss cheese and white cheddar and sprinkle in some freshly grated parmesan cheese. I prefer shredding and grating the cheese from the block for a more authentic taste. Sharp cheddar cheese and Monterey Jack are another excellent option.
- Nutmeg | Boost the flavor with ground nutmeg, adding nuttle and subtly sweet notes. Don’t skip this, it brings out the flavors!
- Salt and pepper | Sprinkle in some kosher salt and black pepper to taste.
- Panko topping | Combine melted butter and panko bread crumbs for a crunchy buttery casserole topping. Omit for gluten-free or use gluten-free panko.
How to Make Easy Broccoli Cauliflower Gratin
Step 1 | Preheat and prep
Start by preheating the oven to 375° F (190° C) and lightly coating a baking dish with oil or butter. Meanwhile, bring a couple of inches of water to a large pot with a steamer basket and boil.
Recommended Tool
- Vegetable Steamer, this is a good sturdy steamer!
Step 2 | Steam the veggies
Next, rinse and cut the broccoli and cauliflower into smaller bite-size florets, then place broccoli and cauliflower florets in the basket in the pot, cover, and simmer until they are crisp tender, for about 3-4 minutes. Remove the basket and allow it to drain.
Fresh Tips
- For the best results, buy the blocks of white cheddar, Swiss, and parmesan cheese and grate them yourself, avoiding the pre-shredded cheese additives that prevent it from melting well.
- Be careful not to overcook the veggies when steaming because they will continue to cook in the oven. No one wants mushy casserole.
Step 3 | Make the au gratin sauce
Now, heat a medium saucepan or a large skillet to medium heat, heat the oil, then add the onions and saute until they are translucent, taking around five minutes. Next, add the garlic and cook for less than a minute until it is fragrant.
Add the flour and stir until the mixture is golden and thick to make a roux. From here, slowly add the half and half, continuously stirring until the sauce thickens.
Finally, lower the heat and stir the cheese in small batches until it has melted into the sauce ingredients—season with nutmeg, salt, and pepper.
Step 4 | Assemble, bake, and serve!
If there’s enough room in the pot, add the steamed broccoli and cauliflower to the sauce and stir gently to coat. Or place drained vegetables in a large bowl, pour the cheese sauce over the top, gently toss to coat.
Then, pour the veggie mixture into the prepared baking dish and move on to the buttery panko topping.
Step 5 | Panko Topping (optional)
In a small bowl, combine the melted butter, breadcrumbs, and two tablespoons of parmesan cheese, sprinkling over the top of the casserole.
Slip the dish into the oven and bake for 25 minutes. Once the casserole is golden brown on top, the dish is ready! Serve piping hot and fresh out of the oven!
Fresh Tips
- Broccoli and cauliflower can be a little bland, so a great way to boost the flavor is to add seasonings and taste as you go.
- If desired, garnish with sliced green onions and freshly grated parmesan cheese.
For easy casserole side dishes, check out my Green Bean Casserole made without mushroom soup and this delicious Homemade Corn Pudding Recipe. Or serve a convenient casserole as the main dish with this Cheesy Hamburger and Tater Tot Casserole or Chicken and Wild Rice Casserole (use your leftover Thanksgiving turkey!)
Variations
If preferred, you can use roasted broccoli and cauliflower too. Roast and then toss in the cheese sauce and bake as directed.
Gluten-Free Broccoli and Cauliflower Casserole
Use a gluten-free brand of panko breadcrumbs and a gluten-free flour alternative in your sauce to make the dish gluten-free. Furthermore, use blocks of cheese rather than pre-shredded packs with additives that often contain gluten. That is it!
Keto Diet Adjustments for Broccoli and Cauliflower Bake
Substitute almond or coconut flour for the wheat flour to make the dish low carb. Skip the panko breadcrumbs altogether, or toss some pork rind crumbs with melted butter and sprinkle on top.
Add Protein to Make it a Main Dish
Add cooked chicken breast, turkey, rotisserie chicken, diced ham, or bacon to the sauce with the vegetables to make this a main dish. Leftover turkey from the holidays works, too!
Vegan Vegetable Au Gratin
All you need to do for a vegan or dairy-free version is replace the cheese, cream, and butter with your favorite plant-based products.
Substitutions
- Half and Half – Heavy cream, Whole milk, 2%, or skim milk can be substituted for half and half. Other than heavy cream, this may make the dish less creamy and rich.
- Additional Vegetables – Add vegetables like sliced carrots, brussels sprouts, asparagus, or peas for added flavor, nutrients, and pops of color.
- Seasoning – Play with various herbs and seasonings, like thyme, rosemary, and paprika, to add depth of flavor.
- Panko – Top your casserole with traditional breadcrumbs, crushed crackers, or crushed potato chips to add a crunchy texture without panko. Or add crunchy french-fried onions to the topping for a classic and delicious twist!
- Nuts – Sprinkle in chopped nuts like almonds or pecans for extra crunch.
- Loaded Cauliflower Broccoli Casserole – Add cream cheese or sour cream for extra thickness and cheesy goodness.
- Ritz Crackers – Trade out the panko topping for crushed Ritz crackers for a buttery good alternative the whole family will love.
Recommended Tools
- I love these Staub oval bakers, great for this vegetable gratin.
Frequently Asked Questions
Dishes topped with cheese and breadcrumbs and baked in the oven are considered au gratin. Like this amazing Potatoes dauphinoise (au gratin).
Yes, you can use frozen broccoli and cauliflower. However, fresh veggies give the dish a crisper texture, while frozen ones will be much softer. So, you may want to take some time off the steaming process and pat the thawed vegetables dry to remove the excess moisture before adding them to the recipe.
Sure! Most casseroles are ideal for making ahead. First, steam the veggies and make the sauce, but keep the two separate until you’re ready to bake the recipe. The two components can be held in the fridge until the next day before they lose flavor and texture.
Before baking, set the ingredients on the countertop to room temperature, then combine, make the topping, and bake as directed.
If you want to make it a week or more ahead, follow the recipe as instructed, but stop when adding the topping. Keep the topping in a separate ziplock bag. Then, remove the dish from the freezer when ready to bake, allow it to thaw, add the topping and bake.
Cauliflower and broccoli casserole is versatile and goes well with various dishes. It’s the perfect side dish for main dishes such as grilled chicken, turkey legs, baked fish, and more.
Storage Tips
Fridge – Save leftovers for 3-4 days by storing them in an airtight container in the refrigerator.
Freeze – You can freeze this casserole in a zipped freezer bag or airtight container for up to 3 months.
How to reheat broccoli and cauliflower casserole
Reheat from the fridge by placing the recipe in an oven-safe dish and heating it at 350° F (175° C) until warm. First, let the recipe thaw in the fridge overnight, then bake it as directed, possibly cooking it for a little longer if the ingredients are extra chilly.
From Frozen: Make sure your dish can go from freezer to oven, remove from freezer while preheating the oven. Sprinkle on panko breadcrumbs, then cover with oil-sprayed aluminum foil and bake 10-15 minutes longer than directions until hot and bubbly, removing the foil the last 15 minutes.
What to Serve with Cheese Broccoli Cauliflower Casserole
Best dinners to serve with broccoli cauliflower gratin
Naturally, we think about turkey and I have some amazing turkey recipes for you. But this dish is also amazing with this Best Cheesy Hamburger Tater Tot Casserole Recipe.
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You can have this easy Roasted Air Fryer Turkey Breast on the table in less than an hour. Loaded with flavor, juicy and tender every time. Use boneless or bone-in turkey breast.
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Best Cheesy Hamburger Tater Tot Casserole Recipe
The whole family will love this cheesy hamburger tater tot casserole! Your kids will clean their plates, the picky teens will ask for more, and the adults will beg for the recipe.
It’s worth the extra effort to steam fresh veggies for this casserole dish, being that they are the stars of the show.
More Vegetable Recipes
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Cheesy Broccoli Cauliflower Casserole (Vegetable Au Gratin)
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Ingredients
- 4 cups broccoli florets fresh is best
- 4 cups cauliflower florets fresh is best
- 2 tablespoons olive oil
- ½ cup onion chopped or minced
- 3 cloves garlic minced or pressed
- 2 tablespoons all-purpose flour or sub with gluten-free all purpose flour or almond flour
- 2 cups half and half sub with heavy cream, whole milk or other % or plant-based milk
- 1 cup Swiss cheese shredded
- 1 cup white cheddar shredded
- ½ cup Parmesan cheese + 2 tablespoons Parmesan cheese, freshly grated and divided
- ¼ teaspoon ground nutmeg try fresh ground, so good
- Salt and pepper to taste
- 2 tablespoons butter melted
- ½ cup panko bread crumbs or gluten-free panko
Instructions
- Preheat the oven to 375° F (190° C). Lightly coat an 8×8, 9×9 or gratin baking dish with oil or butter.
- Add 1-2 inches of water into a large pot fitted with a steamer basket. Bring the water to a boil. Carefully add the broccoli and cauliflower, cover, and simmer until just crisp tender, about 5 minutes. Remove the basket from the pot and allow it to drain.
- Heat a medium saucepan or skillet to medium heat. Add the olive oil, allow it to warm a bit, and then add the onion and saute until translucent, about 5 minutes. Add the garlic and stir until fragrant, 30 seconds.
- Add the flour (or alternative) and stir constantly, until the mixture turns golden and thick.
- Slowly add the half and half, about ½ cup at a time, stirring constantly, adding more as it thickens.
- Once the sauce has thickened, lower the heat, and add the cheeses in small batches and stir until melted.
- Add the nutmeg and stir to combine. Add salt and pepper to taste. I used ½ teaspoon of each.
- Add the steamed broccoli and cauliflower to the sauce and stir to coat. Then pour the mixture into the prepared baking dish.
- Combine the melted butter, breadcrumbs and 2 tablespoons of parmesan cheese in a small bowl. Sprinkle over the top of the casserole.
- Bake for 25 minutes until bubbly and top is slightly golden, serve immediately.
Notes
● Fresh broccoli and cauliflower will give the best texture in this dish.
● Whole milk can be substituted for half and half. You can also use 2% or skim milk, but it will be less creamy and rich.
● Don’t overcook the veggies when steaming; they will cook more in the oven. Overcooking will result in mushy vegetables.
● Add cooked chicken breast to the sauce with the vegetables to make this a main dish.
● Broccoli and cauliflower can be bland vegetables; taste and add more seasoning if necessary. Gluten-Free Broccoli and Cauliflower Casserole | Use a gluten-free brand of panko breadcrumbs and a gluten-free flour alternative in your sauce to make the dish gluten-free. Grate your own cheese, as pre-shredded packs have additives that often contain gluten. That is it! Low-Carb Broccoli and Cauliflower Bake | Substitute almond or coconut flour for the flour to make the dish low-carb. Skip the panko breadcrumbs, or toss some pork rind crumbs with melted butter and sprinkle on top. Add Protein | Add cooked chicken breast, turkey, rotisserie chicken, diced ham, or bacon to the sauce with the vegetables to make this a main dish. Leftover turkey from the holidays works, too! Vegan Vegetable Au Gratin | All you need to do for a vegan or dairy-free version is replace the cheese, cream, and butter with your favorite plant-based products.
Nutrition
I Kathleen, I made your, califlower and broccoli cheesy casserole. Very good. I’m a professional cook in my area of Wisconsin. I’m always looking for new challenges. I’m 80 yrs young. Thank you for sharing your recipes with with the public. Please keep doing your great recipes for all of us
I love that, precious Mary!! That’s how I yearn to be- always looking for new challenges!! Thank you for your sweet words, so glad you loved it. High praising coming from a chef!!
I used whole milk instead of half and half and it gave the perfect amount of creaminess for me. Great recipe!
Love it!!
Such a yummy casserole! The combination of tender broccoli and cauliflower with a creamy sauce and two cheeses is simply irresistible! It’s on our menu for Thanksgiving this year, too.
Yay! So glad you loved it!
Broccoli and cauliflower are perfect together and adding cheese just takes it over the top.
It really does, thanks so much, Ellen!
SO good! We got our kids to both eat broccoli willingly with this one. FOR SURE a keeper!!
YAY! That’s always a huge win!
Who knew veggies would taste so good?! LOVED this as a side dish and my daughter even loved it too. I’ll be adding this to my dinner rotation 🙂 thank you!
Agree!! So glad you loved it, Kathryn!
This is the perfect side dish! So delicious!
YAY! Thanks so much!
This recipe is so good. It’s so creamy and delicious and was the perfect side to our grilled chicken. It made an amazing lunch the next day too!
It does doesn’t it?!!
Even got kids to love this one! Will make again.
A huge win!! Thank you!
Oh yum! Definitely perfect for the upcoming holidays. I especially love the 15 minutes of prep.
Right?! So quick and easy too!
This casserole was the perfect addition to our dinner last night! Low carb and totally delicious!
Thank you Tayler! So glad to hear.
My family always makes a cauliflower dish for Thanksgiving but this year I’m going to swap it for this one. It’s so much more flavorful and exciting to serve!
Everyone will love it!
This cheesy side dish is a family favorite! It’s easy to make and delicious!
Thank you, Holley!