Ingredients:

  • 3 lbs (1.35 kg) Russet or Yukon Gold Potatoes, peeled and sliced 1/8 inch (3 mm) thick
  • 1 cup (115 g) Sharp Cheddar Cheese, shredded
  • 1 cup (115 g) Gruyère Cheese, shredded
  • 1 Tbsp (14 g) Unsalted Butter, for greasing the dish
  • 4 Tbsp (56 g) Unsalted Butter, for the roux
  • 1/4 cup (30 g) All-Purpose Flour
  • 2 cloves Garlic, minced or pressed
  • 2 cups (475 ml) Whole Milk
  • 1 cup (240 ml) Heavy Cream
  • 1 tsp (5 g) Kosher Salt
  • 1/2 tsp (2.5 g) Freshly Ground Black Pepper
  • 1/4 tsp (1 g) Freshly Grated Nutmeg

Instructions:

  1. Preheat oven to 375°F (190°C). Generously grease a 9x13 inch baking dish with 1 Tbsp of butter. Ensure potatoes are sliced uniformly thin (3mm); rinse briefly to remove excess starch if desired, then pat completely dry.
  2. Start the Roux: Melt 4 Tbsp of butter in a large saucepan over medium heat. Add the minced garlic and sauté until fragrant (about 1 minute). Whisk in the flour and cook, stirring constantly, for 1–2 minutes until a smooth, light golden roux forms.
  3. Build the Sauce: Slowly pour in the whole milk and heavy cream while continuously whisking to prevent lumps. Bring the sauce to a gentle simmer, stirring frequently, until the sauce thickens significantly and coats the back of a spoon (about 5–7 minutes).
  4. Season and Incorporate Cheese: Remove the saucepan from the heat. Stir in the salt, pepper, and freshly grated nutmeg. Gradually fold in 1.5 cups (total) of the shredded cheese blend (reserving 0.5 cup for the topping) until the cheese is fully melted and the sauce is smooth and creamy.
  5. Assemble the Gratin: Spread a thin layer of the cheese sauce on the bottom of the prepared baking dish. Arrange one-third of the potato slices in a single, slightly overlapping layer over the sauce. Pour one-third of the remaining sauce evenly over the potatoes. Repeat this layering process twice more, ensuring the top layer is fully covered by the sauce.
  6. Bake (Covered): Cover the dish tightly with aluminum foil and bake for 40 minutes. The potatoes should be fork-tender.
  7. Finish the Gratin: Remove the foil. Sprinkle the remaining 0.5 cup of reserved cheese blend over the top. Return to the oven and bake uncovered for an additional 20–25 minutes, or until the top is bubbling, deeply golden brown, and slightly crispy.
  8. Rest: Remove the dish from the oven and let it rest on a wire rack for a minimum of 15 minutes before serving. This allows the sauce to set for cleaner servings.