Ingredients:

  • 5 lbs Brussels Sprouts, trimmed and halved lengthwise
  • 2 Tbsp Olive Oil
  • 1 tsp Kosher Salt
  • 1/4 tsp Black Pepper, freshly cracked
  • 3 Tbsp Unsalted Butter (for the roux)
  • 3 Tbsp All-Purpose Flour
  • 2 cups Whole Milk, warmed slightly
  • 1 cup Sharp Cheddar Cheese, freshly grated
  • 1/2 cup Gruyère Cheese, freshly grated (for sauce)
  • 1/4 tsp Freshly Grated Nutmeg
  • 1/2 tsp Kosher Salt (for sauce)
  • Pinch of White Pepper
  • 1/2 cup Panko Breadcrumbs
  • 2 Tbsp Melted Unsalted Butter (for topping)
  • 1/4 cup Gruyère Cheese (reserved for the top layer)

Instructions:

  1. Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper.
  2. Toss the halved Brussels sprouts in a large bowl with 2 tablespoons of olive oil, 1 teaspoon of salt, and 1/4 teaspoon of black pepper.
  3. Spread the seasoned sprouts in a single layer, cut-side down, on the prepared baking sheet. Roast for 15 minutes, or until the edges are slightly charred and tender-crisp. Remove and set aside.
  4. Start the Roux: Melt 3 tablespoons of butter in a medium saucepan over medium heat. Whisk in the flour until a smooth paste forms (the roux). Cook for 1–2 minutes, stirring constantly, until the paste smells nutty and looks light blonde.
  5. Add Milk: Gradually whisk in the warm whole milk, pouring slowly to incorporate the roux without lumps. Continue whisking over increased heat until the sauce thickens significantly and coats the back of a spoon (about 5–8 minutes).
  6. Season and Add Cheese: Remove the pan from the heat. Stir in the 1 cup of Cheddar, 1/2 cup of Gruyère, nutmeg, and 1/2 teaspoon of salt. Stir continuously until the cheese is completely melted and the sauce is smooth (this creates the Mornay sauce). Adjust seasoning if necessary.
  7. Pour the pre-roasted Brussels sprouts into a prepared 9x13 inch baking dish. Pour the Mornay sauce evenly over the sprouts.
  8. Prepare the Topping: In a small bowl, combine the Panko breadcrumbs with the 2 tablespoons of melted butter. Scatter the buttery Panko evenly over the gratin.
  9. Sprinkle the reserved 1/4 cup of Gruyère over the Panko layer.
  10. Bake: Place the gratin dish in the 400°F (200°C) oven. Bake for 20–25 minutes, or until the sauce is deeply bubbling and the topping is golden brown and crisp.
  11. Rest and Serve: Remove from the oven and allow to rest for 5–10 minutes before serving, which allows the sauce to set slightly.