Ingredients:

  • 2 lbs (900g) Yukon Gold potatoes, peeled and thinly sliced (about 1/8 inch or 3mm thick)
  • 2 tablespoons (30g) unsalted butter, plus more for greasing the dish
  • 1 medium yellow onion, thinly sliced
  • 2 cloves garlic, minced
  • 2 cups (475ml) heavy cream
  • 1 cup (240ml) whole milk
  • 1/2 teaspoon freshly grated nutmeg
  • 1/4 teaspoon ground white pepper
  • 1 teaspoon kosher salt
  • 1/2 cup (50g) grated Gruyère cheese
  • 1/4 cup (25g) grated Parmesan cheese
  • Fresh thyme sprigs (optional, for garnish)

Instructions:

  1. Peel and thinly slice the potatoes. Soak in cold water while preparing other ingredients to prevent browning. Drain and pat dry before using.
  2. Melt butter in a saucepan over medium heat. Add onion and cook until softened, about 5-7 minutes. Add garlic and cook for another minute until fragrant.
  3. Pour in heavy cream and milk. Add nutmeg, white pepper, and salt. Bring to a simmer, then reduce heat and simmer for 5 minutes, stirring occasionally, until slightly thickened.
  4. Preheat oven to 350°F (175°C). Grease the baking dish with butter. Layer the potato slices in the dish, overlapping slightly. Pour the cream sauce evenly over the potatoes, ensuring all slices are coated.
  5. Sprinkle Gruyère and Parmesan cheese evenly over the top. Bake for 50-60 minutes, or until potatoes are tender and the cheese is golden brown and bubbly.
  6. Let the gratin rest for 10-15 minutes before serving. Garnish with fresh thyme, if desired.