Ingredients:

  • 1.5 lb Brussels sprouts (about 700 g), trimmed and halved (large ones quartered)
  • 1 tablespoon (15 ml) olive oil
  • Salt and freshly ground black pepper
  • 2 tablespoons (28 g) unsalted butter
  • 1 small shallot, finely minced (about 2 tablespoons / 20 g) — optional but recommended
  • 1 garlic clove, minced (optional)
  • 2 tablespoons (16 g) all-purpose flour
  • 1 cup (240 ml) whole milk
  • 1/2 cup (120 ml) heavy cream
  • 1 teaspoon Dijon mustard
  • Pinch freshly grated nutmeg
  • 1/2 teaspoon kosher salt (adjust to taste)
  • 1/4 teaspoon freshly ground black pepper
  • 1 1/2 cups (150 g) grated Gruyère or Comté (or sharp white cheddar) — divided (about 1¼ cup for sauce + ¼ cup for topping)
  • 1/2 cup (50 g) freshly grated Parmesan or Pecorino
  • 1/2 cup (50 g) panko breadcrumbs
  • 1 tablespoon (14 g) unsalted butter, melted (to toss with panko)
  • Zest of 1/2 lemon (optional, for brightness)
  • Optional garnish: chopped fresh parsley or chives
  • Optional add-ins: 4 slices bacon, cooked crisp and crumbled (or 4 oz / 115 g pancetta, rendered)
  • Optional: 1/4 teaspoon red pepper flakes for a touch of heat

Instructions:

  1. Prep the sprouts: Trim stems and halve sprouts (quarter large ones). Toss with olive oil, salt, and freshly ground black pepper.
  2. Par-cook the sprouts: Bring a large pot of salted water to a boil and blanch sprouts 3–4 minutes until bright green and just tender. Shock in ice water, drain, and set aside.
  3. Make the cheese sauce: Melt 2 tablespoons butter in a saucepan over medium heat. Sweat the minced shallot (and garlic, if using) until soft. Whisk in 2 tablespoons flour and cook 1 minute.
  4. Gradually whisk in 1 cup milk and 1/2 cup heavy cream; simmer gently 4–6 minutes until sauce thickens to coat the back of a spoon. Whisk in 1 teaspoon Dijon mustard, a pinch of nutmeg, 1/2 teaspoon kosher salt, 1/4 teaspoon pepper, and 1 cup (about 125 g) grated Gruyère until melted and smooth. Taste and adjust seasoning.
  5. Combine and assemble: Either toss the blanched sprouts with the cheese sauce until evenly coated and transfer to a 2–3 quart gratin dish, or layer sprouts in the dish and pour sauce over, pressing down so sauce settles throughout.
  6. Top with cheese: Sprinkle the remaining Gruyère and grated Parmesan evenly over the sauced sprouts.
  7. Prepare topping: Toss panko with melted butter and lemon zest (if using). Sprinkle panko mixture over the cheese layer. Scatter crumbled bacon if using.
  8. Bake and finish: Bake in a preheated 375°F (190°C) oven for 25–30 minutes until bubbly and sides are set. For a golden top, broil 1–3 minutes, watching closely to avoid burning, until panko and cheese are nicely browned.
  9. Rest and serve: Let the gratin rest 5 minutes before serving to allow the sauce to thicken slightly. Garnish with chopped parsley or chives if desired.