This make-ahead broccoli and cauliflower casserole has delicious creamy cheddar leek sauce and crunchy panko breadcrumb topping. It can be prepared a day ahead or you can make it and serve it right away.

a white casserole dish with broccoli and cauliflower casserole with browned breadcrumbs on top

I originally published this recipe on November 13th, 2015. I have updated some of the content to share it with you today. This post contains affiliate links.


How To Make Broccoli and Cauliflower Casserole

Blanch and Shock the Broccoli and Cauliflower

The step of cooking the vegetables and then shocking it in ice water is important so that the cauliflower and broccoli doesn’t keep cooking when it is mixed with the cheese sauce. Otherwize it would become more watery, sulfuric and  would turn an army green color we’re trying to avoid.

  • Begin by bringing a large pot of salted water to a boil for blanching the vegetables. As I mentioned in this recipe for make-ahead Orange Ginger Green Beans, blanching is a term that means cooking in boiling water for a short time, until the veggies are bright green and still crisp tender. 
  • Set Up Ice Bath: Next you’ll want to plunge the cauliflower and broccoli into a bowl of ice water. 
  • Cook In Two Batches or All Together: If you have a large enough pot, you can blanch them in the same pot, or you can do them in two batches.
  • Boil: Add the broccoli and cauliflower to the boiling water and stir to submerge it in the water. Boil for 3 minutes, stirring occasionally so that it cooks evenly.
  • Shock: Then using a strainer, transfer the cauliflower and broccoli to the ice bath. 
  • Drain: Let the Veggies Cool in the Ice Bath for Several Minutes before draining well. It’s important not to have excess moisture in this recipe as it will make the sauce watery. So just leave the veggies in the colander to drain for a few minutes.

Make The Cheddar Leek Sauce

The cheddar leek cheese sauce in this casserole is really delicious and creamy. If you have made stove top macaroni and cheese before you will be pretty familiar with the cooking technique. 

Not that this cheese sauce is thick when you are done making it in the saucepan. This is by design, because the cauliflower and broccoli let off extra liquid as they bake with the sauce so the sauce thins out perfectly by the time it is all done.

Why the flour? The flour in the sauce thickens it and makes it so that the cheese melts in smoothly. Without it (or an alternative starch) the cheese would become clumpy and would look curdled or would “break.” This way the sauce coats the vegetables much better with this thickener.

broccoli and cauliflower casserole in a white ceramic casserole dish with handles

Steps To Make This Recipe

How To Make This Broccoli and Cauliflower Gratin Gluten Free

To make this gluten free, you’ll need to change up the sauce technique slightly. Here’s how:

  1. Cook the leeks as directed. 
  2. Add 1 1/2 cups milk and heat until just steaming.
  3. Whisk the remaining 1/2 cup milk with 2 tablespoons plus 1 teaspoon cornstarch in a small bowl.
  4. Drizzle the cornstarch slurry into the steaming leek and milk mixture while whisking. Bring to a simmer while whisking.
  5. Remove from the heat and stir in the cheese and pepper.

You will also have to purchase gluten-free panko. I like Ian’s brand

How To Make Lactose Free Cheese Sauce

To make this casserole lactose free, use a lactose free milk such as lactaid or Organic Valley Lactose Free milk and Cabot Cheddar (which is lactose free.)

Substituting Other Vegetables

You can use all cauliflower or all broccoli if you like. You could also substitute in halved Brussels sprouts for one or the other, but note that you will need to blanch it for 4 minutes 30 seconds.

a white casserole dish with broccoli and cauliflower casserole with browned breadcrumbs on top with a spoon in it

How to Make This Casserole Ahead of Time

This recipe can easily be prepped in advance and cooked just before you plan on serving it.  To make this casserole ahead of time:

  1. You’ll need to make the cheese sauce and blanch the veggies as directed in the recipe.
  2. Then combine everything and transfer to your casserole dish.
  3. Cover the casserole in foil and refrigerate up to 24 hours in advance. (note; do not add the breadcrumbs yet as they will pull too much moisture out of the casserole and will not crisp up again.)
  4. Cook the casserole covered for 25 minutes.
  5. Remove the cover, top with the breadcrumb mixture and bake until the casserole is hot all the way through, the sauce is bubbling and the vegetables are tender, 28 to 35 minutes.

More Broccoli and Cauliflower Side Dish Recipes

This Roasted Broccoli and Cauliflower with cheese is a simple side dish for weeknights or the holidays. 

This simple steamed cauliflower with herbs is about as basic as it gets.

This lemon garlic broccoli is a popular recipe and one of my daughters all time favorite side dishes. 

This Broccoli Mash with garlic is a great alternative and low carb side dish. 

Want more ideas for cauliflower? Don’t miss this Ultimate Guide to Cauliflower.

More Casserole Recipes:

This is a great way to use up leftover turkey after Thanksgiving or for leftover chicken Chicken and Biscuits Casserole.

This is a great no canned soup comfort food meal that always gets great reviews: Chicken and Rice Casserole.

This lower carb and veggie heavy Zucchini Casserole is a great way to use up a lot of zucchini. 

Here’s another cheesy holiday side which can be made ahead: Cheddar Green Bean Casserole.

Easy Fish Casserole: They say not to eat fish and cheese, but that’s because they’ve never tried this recipe inspired by my grandmother’s recipe. 


Thanks so much for reading! If you make this recipe, please come back and let me know by leaving a star rating and review! 

Happy Cooking!



Healthy Make-ahead Broccoli and Cauliflower Casserole with Creamy Cheddar Leek Sauce and Crunchy Panko Breadcrumb topping on

broccoli and cauliflower casserole

  • Author: Katie Webster
  • Prep Time: 30 minutes
  • Cook Time: 30 minutes
  • Total Time: 1 hour 15 minutes
  • Yield: 10 cups 1x
  • Category: Side Dish
  • Method: Baked
  • Cuisine: American


This make-ahead broccoli and cauliflower casserole is a healthy and delicious option for a covered dish for the holidays. The cauliflower and broccoli are coated in a creamy leek cheddar sauce and topped with crunchy panko breadcrumb topping.



  • 1 medium head of cauliflower
  • 2 large broccoli crowns (1 pound)
  • 2 tablespoons plus 1 teaspoon extra-virgin olive oil, divided
  • 1 large leek, white and pale green part only, sliced and washed
  • ¾ teaspoon salt
  • 1/3 cup all-purpose flour
  • 2 cups fat-free milk (lactose-free if desired)
  • 6 ounces sharp lactose free cheddar, shredded (I used Cabot Alpine)
  • ¼ teaspoon ground white pepper
  • ¼ cup panko, preferably whole-wheat
  • 1 teaspoon paprika
  • ¼ teaspoon garlic powder


  1. Bring a large pot of salted water to a boil. Set a large bowl of ice water to the side.
  2. Core cauliflower and cut into medium florets. Cut off broccoli stems and cut into florets. Blanch cauliflower 3 minutes in boiling water. Remove from the water with a slotted spoon or small strainer and transfer immediately to the ice bath to stop it from cooking. Repeat with the broccoli, cooking for 3 minutes, and shocking in the ice bath. Drain the vegetables very well. Reserve bowl for mixing in step 4.
  3. Prepare cheese sauce. Heat 2 tablespoons oil in a large saucepan over medium-high heat. Add leek and ¾ teaspoon salt and cook, stirring often until the leek is soft, 4 to 5 minutes. Sprinkle the flour over the leek and stir to coat. Add milk and bring to a simmer, over high heat, stirring constantly. Cook until bubbling and thickened, 1 to 2 minutes longer. Remove from heat and stir in cheese and pepper until the cheese is completely melted into the sauce.
  4. Preheat oven to 350 degrees F. Coat a 2 ½ quart baking dish with cooking spray. Stir panko, the remaining 1 teaspoon oil, paprika and garlic powder in a small dish until evenly moist. Mix the vegetables and cheese sauce together in the reserved bowl. Transfer to the prepared baking dish.
  5. Top with the panko mixture. Bake until the casserole is hot all the way through, the sauce is bubbling and the vegetables are tender, 28 to 35 minutes. Let cool 15 minutes before serving.


TO MAKE AHEAD: Prepare through step 4 (do not pre-heat oven in step 4.) Cover casserole in foil and refrigerate up to 24 hours in advance. Preheat oven, and bake casserole covered for 25 minutes. Remove foil and continue with topping with the breadcrumb mixture and baking as directed in step 5.


  • Serving Size: 1 cup
  • Calories: 171
  • Sugar: 3 g
  • Sodium: 377 mg
  • Fat: 10 g
  • Saturated Fat: 5 g
  • Carbohydrates: 12 g
  • Fiber: 2 g
  • Protein: 8 g