The holidays are filled with starchy and indulgent foods, but this broccoli and cauliflower gratin offers some respite. It has all that creamy and cheesy flavor but with way fewer carbs and way more vitamins and minerals. It still feels rich and indulgent, but I like knowing that I am still being somewhat healthy when I enjoy this broccoli cauliflower casserole.
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This broccoli and cauliflower gratin recipe only takes about 30 minutes from start to finish! Cauliflower is my go-to vegetable when I need something to replace starchy potatoes. It helps cut down on carbs and create a healthier version of au gratin potatoes. But the cheese sauce is the real star of the show– so creamy, dreamy, and delicious. This broccoli cauliflower casserole tastes just like my favorite holiday side, but healthier!
What’s in This Broccoli and Cauliflower Gratin Recipe?
- Bread: A little bit of day-old white or wheat sandwich bread grinds up to create the perfect crispy topping. If you prefer, you can use ¾ cup of store-bought Italian breadcrumbs instead.
- Butter: Unsalted butter helps bind the topping and adds moisture and richness to the casserole.
- Broccoli + Cauliflower: These brassicas are the star of the show! They have a great texture when cooked and are much healthier than a traditional potato dish.
- Onion + Garlic: Create a savory base of flavor for the casserole.
- Flour: All-purpose flour helps thicken the cheese sauce.
- Heavy Cream: Creates a rich and creamy sauce.
- Broth: Low-sodium chicken broth or dry white wine helps add tons of flavor to the sauce.
- Spices: Nutmeg, mustard powder, and red pepper flakes enhance the overall flavor of the cheese sauce and add a touch of spice.
- Cheese: I like Parmesan and sharp cheddar cheese, but you can swap the cheddar for a different melting cheese if you prefer.
Tips for Success
- I have made this dish successfully with frozen broccoli and cauliflower. I used one bag of each and cooked them in the microwave according to the package instructions.I like the steam fresh kind best.
- Make sure to pat the broccoli and cauliflower dry before stirring into the cheese sauce. Wet veggies can introduce extra moisture that will cause the casserole to turn watery as it bakes.
- I made a roux out of butter and flour to help thicken up the sauce and bind it together. This prevents the sauce from splitting, so long as you don’t put it over too high of heat!
How to Store and Reheat
Store leftover broccoli and cauliflower gratin tightly wrapped with plastic wrap or aluminum foil in the refrigerator for up to 4 days. Reheat in a 350°F oven for 20-30 minutes, or until warmed through. I do not recommend freezing this dish, as the texture changes too much once thawed.
Serving Suggestions
I like to serve this broccoli cauliflower casserole alongside my favorite holiday mains, like Thanksgiving turkey, brown sugar glazed ham, or beef tenderloin! Add some holiday sides and you’ve got the perfect dinner!
Broccoli Cauliflower Casserole Recipe
Equipment
- 11×7-inch Baking Pan
Ingredients
For the Topping
- 3 slices sandwich bread white or wheat; a little dry is best
- 2 tablespoons unsalted butter room temperature (¼ stick)
- ¼ teaspoon table salt
- ⅛ teaspoon freshly ground black pepper
For the Filling
- 1 head cauliflower (about 1½ pounds)
- 1 head broccoli (about 1 pound)
- 1 tablespoon table salt plus more to taste
- 2 tablespoons unsalted butter (¼ stick)
- ¼ yellow onion diced (about 2 tablespoons)
- 1 clove garlic minced
- 1½ tablespoons all-purpose flour
- 1¼ cups heavy cream
- ¼ cup low-sodium chicken broth or dry white wine
- 2 pinches freshly grated nutmeg
- 1 teaspoon dry mustard powder
- 1 teaspoon crushed red pepper flakes
- ⅛ teaspoon freshly ground black pepper
- ½ cup freshly grated Parmesan cheese
- 1 cup freshly shredded sharp cheddar cheese
Instructions
- Preheat oven to 425°F and set the oven rack to the middle position. Spray a 2-quart (11×7-inch) casserole dish with nonstick cooking spray.
- Tear each slice of bread into 4 pieces.3 slices sandwich bread
- Place the bread, butter, salt, and pepper in a food processor fitted with a metal blade. Process until coarse crumbs form, about ten 1-second pulses. Set aside.2 tablespoons unsalted butter, ¼ teaspoon table salt, ⅛ teaspoon freshly ground black pepper
- Trim the cauliflower and broccoli into ¾-inch florets. If using broccoli stalks, use only ½-inch of stalk next to the floret.1 head cauliflower, 1 head broccoli
- Fill a Dutch oven or stockpot two-thirds full with water. Add 1 tablespoon of salt and bring the water to a boil. Stir the boiling water and add the cauliflower and broccoli. Cook until the vegetables have a slight bite, 3-4 minutes, and drain.1 tablespoon table salt
- Heat a large skillet over medium heat. Add butter and cook just until foaming subsides.2 tablespoons unsalted butter
- Add the onion and cook until softened and translucent, 2-3 minutes.¼ yellow onion
- Add the garlic and cook for 30 seconds.1 clove garlic
- Sprinkle the flour over the onion/garlic mixture; stir and cook for about 1 minute.1½ tablespoons all-purpose flour
- Reduce the heat to medium-low and whisk in the cream and broth (or wine). While stirring, bring to a boil.1¼ cups heavy cream, ¼ cup low-sodium chicken broth
- Reduce heat to low and add nutmeg, dry mustard, red pepper flakes, and black pepper. Cook (and stir) just until the mixture has thickened a little. Add salt to taste if needed.2 pinches freshly grated nutmeg, 1 teaspoon dry mustard powder, 1 teaspoon crushed red pepper flakes, ⅛ teaspoon freshly ground black pepper
- Add both cheeses and stir until cheese is melted.½ cup freshly grated Parmesan cheese, 1 cup freshly shredded sharp cheddar cheese
- Remove from the heat and add the cauliflower and broccoli; stir gently to coat the vegetables
- Transfer cauliflower/broccoli mixture to the prepared dish and sprinkle with the breadcrumb topping.
- Bake at 425°F for 15-20 minutes or until the sauce bubbles around the edges and the top is golden brown. Serve immediately.
Video
Becky’s Tips
Nutrition information is automatically calculated, so should only be used as an approximation.
Did you make this? Leave a comment!
How to Make Broccoli and Cauliflower Gratin Step by Step
Prep: Preheat your oven to 425°F and set the oven rack to the middle position. Spray a 2-quart (11×7-inch) casserole dish with nonstick cooking spray.
Make the Topping: Tear 3 slices of sandwich bread into 4 pieces. Place the bread, 2 tablespoons of unsalted butter, ¼ teaspoon of table salt, and ⅛ teaspoon of ground black pepper in a food processor fitted with a metal blade. Process until coarse crumbs form, about ten 1-second pulses. Set aside.
Chop the Veggies: Trim 1 head each of cauliflower and broccoli into ¾-inch florets. If using broccoli stalks, use only ½-inch of stalk next to the floret.
Boil the Veggies: Fill a Dutch oven or stockpot two-thirds full with water. Add 1 tablespoon of table salt and bring the water to a boil. Stir the boiling water and add the cauliflower and broccoli. Cook until the vegetables have a slight bite, 3-4 minutes, and drain.
Cook the Onion and Garlic: Heat a large skillet over medium heat. Add 2 tablespoons of unsalted butter and cook just until foaming subsides. Add ¼ of a diced yellow onion and cook until softened and translucent, 2-3 minutes, then add 1 minced clove of garlic and cook for 30 seconds.
Make the Roux: Sprinkle 1½ tablespoons of all-purpose flour over the onion/garlic mixture; stir and cook for about 1 minute.
Add the Liquids: Reduce the heat to medium-low and whisk in 1¼ cups of heavy cream and ¼ cup of low-sodium chicken broth (or wine). While stirring, bring to a boil.
Season the Sauce: Reduce the heat to low and add 2 pinches of freshly grated nutmeg, 1 teaspoon of dry mustard powder, 1 teaspoon of crushed red pepper flakes, and ⅛ teaspoon of freshly ground black pepper. Cook (and stir) just until the mixture has thickened a little. Add salt to taste if needed.
Add the Cheese: Add ½ cup of freshly grated Parmesan cheese and 1 cup of freshly shredded sharp cheddar cheese and stir until cheese is melted.
Stir in the Veggies: Remove from the heat and add the cauliflower and broccoli; stir gently to coat the vegetables.
Bake the Casserole: Transfer the cauliflower/broccoli mixture to the prepared dish and sprinkle with the breadcrumb topping. Bake at 425°F for 15-20 minutes or until the sauce bubbles around the edges and the top is golden brown. Serve immediately.
Made this before and everybody loved it
I’m so glad to hear that, Evelyn!