Brussel Sprout Casserole

5 from 146 votes

Easy to make, this creamy and cheesy Brussel sprout casserole is a crowd pleasing side dish. Serve up the vegetarian gratin for Thanksgiving!

Cuisine American

Prep Time 15

Cook Time 35

Total Time 50

Servings servings

Calories 143kcal

Preheat the oven to 425°F.
Place brussel sprouts on an 8 x 11 rimmed baking dish, drizzle with olive oil and season with salt, pepper and garlic powder. Toss to coat evenly, and then roast until golden brown, about 20-25 minutes, tossing halfway through.
In a small saucepan over medium heat, melt the butter. Add the onions and cook until translucent, about 3-5 minutes. Add the flour and mustard powder and stir until the flour dissolves, about 1-2 minutes. Slowly pour the milk and stir with a wooden spoon until the sauce thickens. Add ¼ cup gruyere cheese and stir until well blended.
When the brussel sprouts are done roasting, pour the sauce over the brussel sprouts. Sprinkle remaining gruyere cheese on top.
Return the brussel sprouts to the oven and cook until the cheese is melted and bubbly, about 15 more minutes. Serve warm.

Storage: Store any leftovers in an airtight container. They will last up to 3 days in the fridge.

Substitutes: For best results, follow the recipe as is. However here are some common substitutes that would work well in this recipe.

Instead of regular milk, you can use any unsweetened plant-based milk.
Instead of gruyere cheese, you can use shredded cheddar cheese or another one you like.
To make this gluten-free, use an all-purpose gluten-free flour mix. You can also substitute with almond flour.