Ingredients:

  • 2.5 lbs (1.1 kg) Yukon Gold potatoes, peeled and thinly sliced
  • 1 medium yellow onion, thinly sliced
  • 2 cloves garlic, minced
  • 2 tablespoons (30 ml) olive oil
  • Salt and freshly ground black pepper to taste
  • 4 tablespoons (57g) unsalted butter
  • 4 tablespoons (30g) all-purpose flour
  • 3 cups (710 ml) whole milk
  • 1/2 teaspoon ground nutmeg
  • 1 teaspoon Dijon mustard
  • 2 cups (225g) shredded cheddar cheese
  • 1 cup (115g) shredded Gruyere cheese (or Swiss)
  • 1/4 cup (25g) grated Parmesan cheese (Optional)
  • 2 tablespoons breadcrumbs (panko or regular) (Optional)
  • 1 tablespoon melted butter (Optional)

Instructions:

  1. Heat olive oil in a large pan. Add onions and garlic and sauté until softened. Season with salt and pepper. Add the potatoes and cook for a few minutes.
  2. Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1-2 minutes, making a roux.
  3. Gradually whisk in milk, stirring constantly to prevent lumps. Bring to a simmer and cook until thickened, about 5-7 minutes.
  4. Remove from heat and stir in nutmeg, Dijon mustard, cheddar cheese, and Gruyere cheese until melted and smooth. Season with salt and pepper to taste.
  5. Layer half of the potato/onion mixture into the prepared baking dish. Pour half of the cheese sauce over the potatoes. Repeat layers with remaining potatoes and cheese sauce.
  6. In a small bowl, combine Parmesan cheese, breadcrumbs, and melted butter. Sprinkle evenly over the casserole (Optional).
  7. Bake in a preheated oven at 375°F (190°C) for 45-50 minutes, or until the potatoes are tender and the top is golden brown and bubbly. Let stand for 10 minutes before serving.
  8. Let the dish cool and serve to a warm temperature.