Ingredients:

  • 2 lbs (900g) Yukon Gold Potatoes, peeled and thinly sliced
  • 1 teaspoon (5g) kosher salt, plus more to taste
  • ½ teaspoon (2.5g) freshly ground black pepper, plus more to taste
  • 2 tablespoons (30ml) unsalted butter
  • 1 medium yellow onion, finely chopped (about 1 cup/150g)
  • 2 cloves garlic, minced
  • 2 tablespoons (15g) all-purpose flour
  • 2 cups (475ml) whole milk
  • 1 cup (235ml) heavy cream
  • ½ teaspoon (2.5ml) ground nutmeg
  • ½ cup (50g) grated Gruyère cheese
  • ½ cup (50g) grated Parmesan cheese

Instructions:

  1. Preheat oven to 375°F (190°C). Slice potatoes evenly and season generously with salt and pepper.
  2. Melt butter in a saucepan over medium heat. Sauté onion until softened and translucent. Add garlic and cook until fragrant (about 30 seconds).
  3. Whisk in flour until smooth. Gradually whisk in milk and cream, ensuring no lumps form. Bring to a simmer, stirring constantly.
  4. Reduce heat to low. Simmer until sauce thickens slightly. Stir in nutmeg, Gruyère, and Parmesan cheese until melted and smooth. Season to taste with salt and pepper.
  5. Arrange a layer of potato slices in the baking dish, overlapping slightly. Pour a portion of the cream sauce over the potatoes. Repeat layering until all potatoes and sauce are used, ending with a layer of sauce.
  6. Bake uncovered for 55-65 minutes, or until potatoes are tender and the top is golden brown and bubbly. Let rest for 10 minutes before serving.