Ingredients:

  • 3 lbs Yukon Gold potatoes, peeled and thinly sliced
  • 1 tbsp melted butter
  • 4 tbsp unsalted butter
  • 3 tbsp all-purpose flour
  • 3 cloves garlic, minced
  • 2 cups heavy cream
  • 1 cup whole milk
  • 1 tsp Dijon mustard
  • 1/4 tsp ground nutmeg
  • 1 tsp kosher salt
  • 1/2 tsp black pepper
  • 1 1/2 cups Gruyère cheese, shredded
  • 1/2 cup Parmesan cheese, finely grated
  • 1 tbsp fresh parsley, chopped

Instructions:

  1. Preheat the oven to 375°F (190°C) and grease a 9x13 inch baking dish with melted butter.
  2. Use a mandoline to slice potatoes into consistent 1/8-inch rounds.
  3. In a saucepan over medium heat, melt 4 tbsp of butter, whisk in the flour, and cook for 1–2 minutes until slightly nutty.
  4. Add minced garlic and sauté for 30 seconds until fragrant.
  5. Slowly whisk in the heavy cream and milk. Simmer for 3–5 minutes, stirring constantly, until the sauce thickens enough to coat the back of a spoon.
  6. Stir in the Dijon mustard, nutmeg, salt, and pepper, then remove from heat.
  7. Arrange a third of the sliced potatoes in the bottom of the dish, pour over a third of the cream sauce, and repeat the layers twice more, ending with sauce.
  8. Evenly sprinkle the Gruyère and Parmesan cheese over the top.
  9. Cover the dish and bake until potatoes are tender, then uncover to brown the crust.