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Cauliflower Gratin is an easy side dish you're sure to love! This Cheesy Broccoli Cauliflower Recipe is absolutely delicious. Be sure to add Cauliflower Broccoli au Gratin to your holiday table!

Broccoli Cauliflower Casserole Recipe

Course: Side Dish
Cuisine: American
Prep Time: 10 minutes
Cook Time: 20 minutes
Total Time: 30 minutes
Servings: 8
Calories: 350kcal
Author: Becky Hardin
This broccoli and cauliflower gratin is cheesy, creamy, and easy to make. You're going to love this broccoli cauliflower casserole recipe for Thanksgiving, Christmas, Easter, and more!
Step-by-step photos can be seen below the recipe card.
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Equipment

Ingredients

For the Topping

  • 3 slices sandwich bread white or wheat; a little dry is best (see note)
  • 2 tablespoons unsalted butter room temperature (¼ stick)
  • ¼ teaspoon table salt
  • 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
  • tablespoons all-purpose flour
  • 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
  • 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 (11x7-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
    A frying pan with broccoli and cauliflower gratin.
  • 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
    A person is holding a baking pan full of broccoli and cauliflower, preparing a delicious broccoli cauliflower casserole.
  • 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.
    A cauliflower gratin dish served with a wooden spoon.

Video

Notes

  • Note: If you prefer, you can use ¾ cups of store-bought Italian Bread Crumbs instead of dry bread.
  • You can also use frozen broccoli and cauliflower. If using, use one bag of each and cook in the microwave according to package instructions. Pat dry before stirring into the cheese sauce. I like the steam fresh kind best.
Storage: Store broccoli cauliflower casserole tightly covered in the refrigerator for up to 4 days. 

Nutrition

Calories: 350kcal | Carbohydrates: 19g | Protein: 12g | Fat: 27g | Saturated Fat: 16g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 7g | Trans Fat: 0.2g | Cholesterol: 77mg | Sodium: 684mg | Potassium: 647mg | Fiber: 5g | Sugar: 5g | Vitamin A: 1466IU | Vitamin C: 119mg | Calcium: 264mg | Iron: 2mg