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creamy brussels sprouts potato gratin

Brussels Sprouts Potato Gratin Casserole

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Prep Time 20 minutes
Cook Time 50 minutes
Resting Time 10 minutes
Total Time 1 hour 20 minutes
Course Dinner
Cuisine American
Servings 6 servings

Equipment

  • 1 9x13 inch baking dish
  • 1 Large pot
  • 1 large skillet
  • 1 Mixing bowl
  • 1 Whisk
  • 1 Chef's knife
  • 1 Cutting board
  • 1 box grater
  • 1 measuring cup
  • 4 Measuring spoons
  • 1 aluminum foil sheet

Ingredients
  

  • 1 1/2 pound Brussels sprouts trimmed and halved
  • 1 1/2 pound Yukon Gold potatoes thinly sliced
  • 2 tablespoon unsalted butter divided
  • 1 tablespoon olive oil
  • 1 small yellow onion thinly sliced
  • 3 clove garlic minced
  • 1 1/2 cup heavy cream
  • 1/2 cup whole milk
  • 1 teaspoon Dijon mustard
  • 1 teaspoon kosher salt plus more to taste
  • 1/2 teaspoon black pepper freshly ground
  • 1/4 teaspoon ground nutmeg
  • 1 1/2 cup Gruyère cheese shredded
  • 1/2 cup Parmesan cheese grated
  • 2 tablespoon fresh thyme leaves chopped
  • 1/4 cup panko breadcrumbs optional
  • 1 tablespoon parsley chopped for garnish

Instructions
 

  • Preheat the oven to 400°F and butter the baking dish with 1 tablespoon of the butter.
  • Bring a large pot of salted water to a boil, add the Brussels sprouts, and blanch for 3 minutes before draining and patting dry.
  • Heat olive oil and the remaining 1 tablespoon butter in a skillet over medium heat, add onion, and cook until soft and lightly golden, about 6 minutes.
  • Stir in garlic and cook for 30 seconds until fragrant, then remove from heat.
  • In a mixing bowl whisk together heavy cream, milk, Dijon, salt, pepper, nutmeg, and thyme.
  • Layer half the sliced potatoes in the baking dish, slightly overlapping, and season lightly with salt and pepper.
  • Scatter half the Brussels sprouts and half the sautéed onions over the potatoes, then sprinkle with half the Gruyère.
  • Repeat layers with remaining potatoes, Brussels sprouts, onions, and Gruyère.
  • Pour the cream mixture evenly over the layered vegetables, tapping the dish gently to settle.
  • Combine Parmesan with panko if using and sprinkle evenly over the top.
  • Cover the dish loosely with foil and bake for 25 minutes.
  • Remove the foil and continue baking until the top is deeply golden and the potatoes are tender when pierced, 20 to 25 minutes more.
  • Let the gratin rest for 10 minutes to set before garnishing with parsley and serving.

Notes

For the best texture, slice potatoes 1/8-inch thick using a sharp knife or mandoline so they cook evenly with the Brussels sprouts. Blanching the sprouts tames bitterness and prevents excess moisture from watering down the cream. If you prefer a lighter dish, substitute half-and-half for the cream and increase the bake time slightly until the center bubbles. Smoked Gruyère or sharp white cheddar adds depth, and a pinch of red pepper flakes gives gentle heat. The gratin can be assembled up to a day ahead, covered, and refrigerated; add 10–15 minutes to the covered bake time if starting cold. Leftovers reheat well at 350°F covered for 15–20 minutes or microwaved in short bursts to keep the sauce from splitting.
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