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Cheesy Brussels Sprouts Gratin Casserole

A comforting casserole featuring tender Brussels sprouts in a rich and creamy cheese sauce topped with a crispy breadcrumb layer.
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Prep Time 15 minutes
Cook Time 50 minutes
Total Time 1 hour 5 minutes
Servings: 8 servings
Course: Side Dish, Vegetable
Cuisine: American, Comfort Food
Calories: 180
Ingredients Method Notes

Ingredients
  

Vegetable Base
  • 2 lb Brussels sprouts, trimmed and halved Quarter or cut into thirds if very large for even cooking.
  • 1/2 cup yellow onion, finely diced Adds sweetness and depth to the dish.
Creamy Sauce
  • 1 tbsp unsalted butter Base for the cheese sauce.
  • 2 tbsp all-purpose flour Thickener for the sauce.
  • 1 1/2 cups 2% milk Can be substituted with half-and-half or whole milk.
  • 1 tbsp fresh thyme, chopped Fresh herb for flavor; can replace with dried thyme.
  • 1/4 tsp ground black pepper For seasoning.
  • pinch ground nutmeg Optional spice for extra flavor.
  • 3/4 tsp kosher salt, divided 1/2 tsp for the sprouts, 1/4 tsp for the sauce.
Toppings
  • 1/2 cup freshly grated Gruyère Sharp white cheddar or another melty cheese can be used.
  • 1/4 cup whole wheat breadcrumbs Can substitute with panko for a crispier top.
  • 3 slices thick-cut bacon Adds smokiness; can be replaced with turkey bacon or ham.
  • Olive oil cooking spray To lightly spray the topping.

Method
 

Preparation
  1. Preheat your oven to 400°F and lightly spray an 8x12-inch (2-quart) gratin dish with cooking spray.
Cooking the Bacon
  1. Cook the bacon in a large skillet over medium-low heat for 8 to 10 minutes until crisp, then transfer to a paper towel-lined plate.
  2. Pour off all but 1 tablespoon of the bacon drippings.
Cooking the Vegetables
  1. Increase heat to medium-high, add Brussels sprouts, onion, and 1/2 teaspoon salt, cooking for 10 to 12 minutes until soft and golden.
  2. Add 1/2 cup water, bring to a boil, then cook for 2 to 3 minutes until evaporated. Transfer vegetables to the baking dish.
Making the Cheese Sauce
  1. Melt the butter in the skillet over medium heat, whisk in flour, and cook for about 1 minute until golden.
  2. Add the milk gradually while whisking, letting it simmer for 2 to 4 minutes until thick enough to coat a spoon.
  3. Stir in thyme, black pepper, nutmeg, and the remaining salt. Remove from heat and stir in Gruyère until melted.
Assembling the Casserole
  1. Pour the sauce over the Brussels sprouts, spreading it evenly.
  2. Sprinkle breadcrumbs on top, lightly spray with oil, and crumble the bacon over everything.
Baking
  1. Bake for 10 to 15 minutes until bubbly and the topping is golden.
  2. Serve hot.
Make Ahead, Store, or Freeze
  1. To make ahead, complete up to Step 5, cover, and refrigerate for up to a day. Bring to room temperature before baking.
  2. Store leftovers in an airtight container in the refrigerator for up to 3 days or freeze for up to 2 months.
  3. Reheat in the oven at 350°F or microwave smaller portions.

Notes

Avoid overcooking Brussels sprouts; they should be crisp-tender before baking. Do not skip the breadcrumb topping and light spray of oil for a golden finish.