Ingredients:

  • 5 lbs Brussels Sprouts, trimmed and halved
  • 2 Tbsp Olive Oil
  • Kosher Salt & Freshly Ground Black Pepper, to taste
  • 3 Tbsp Unsalted Butter
  • 3 Tbsp All-Purpose Flour
  • 2 cups Whole Milk (warmed slightly)
  • A generous pinch of Nutmeg
  • 1 tsp Dijon Mustard
  • 1 cup Gruyère Cheese, freshly grated
  • 1/2 cup Parmesan Cheese, freshly grated
  • 1/2 cup Panko Breadcrumbs
  • 1 Tbsp Melted Unsalted Butter
  • Optional Garnish: Fresh parsley, chopped

Instructions:

  1. Preheat oven to 400°F (200°C). Toss halved Brussels sprouts with olive oil, salt, and pepper. Spread in a single layer on a baking sheet and roast for 15-20 minutes until slightly tender and caramelized.
  2. While sprouts roast, melt 3 Tbsp butter in a medium saucepan over medium heat. Whisk in the flour for 1 minute to create a roux.
  3. Gradually whisk in the warm milk until smooth. Bring to a gentle simmer, whisking constantly, until the sauce thickens enough to coat the back of a spoon (about 5-7 minutes).
  4. Remove the saucepan from the heat. Stir in the Dijon mustard and nutmeg. Slowly fold in the Gruyère and Parmesan until fully melted and smooth. Taste and adjust salt and pepper.
  5. Place the roasted sprouts into a prepared baking dish (approx. 9x13 inch). Pour the Mornay sauce evenly over the sprouts, ensuring they are well coated.
  6. In a small bowl, toss the Panko breadcrumbs with 1 Tbsp melted butter. Sprinkle evenly over the top of the gratin.
  7. Bake uncovered for 10-15 minutes, or until the sauce is bubbly around the edges and the topping is deep golden brown.
  8. Let the gratin rest for 5 minutes before garnishing with fresh parsley and serving hot.