Ingredients:

  • 3 lbs (1.36 kg) Russet or Yukon Gold potatoes, peeled
  • 4 Tbsp (56g) unsalted butter, divided
  • 4 Tbsp (30g) all-purpose flour
  • 3 cups (710 ml) whole milk, warmed
  • 1 cup (240 ml) heavy cream
  • 1/4 tsp ground nutmeg
  • 1 1/2 tsp kosher or sea salt, plus extra for seasoning layers
  • 1/2 tsp freshly ground black pepper
  • 1 cup (115g) shredded Gruyère cheese
  • 1 cup (115g) shredded sharp Cheddar cheese
  • 1 garlic clove, halved (for rubbing dish)

Instructions:

  1. Preheat oven to 375°F (190°C). Rub the inside of a 9x13 inch baking dish generously with the cut side of the garlic clove (discard the clove). Slice potatoes very thinly (about 1/8 inch or 3mm thick). Do not rinse the sliced potatoes.
  2. In a saucepan over medium heat, melt 3 Tbsp of the butter. Whisk in the flour and cook for 2 minutes to create a roux.
  3. Gradually whisk in the warm milk until smooth. Bring to a gentle simmer, whisking constantly, until the sauce thickens enough to coat the back of a spoon (about 5-7 minutes).
  4. Remove from heat. Stir in the heavy cream, nutmeg, salt, and pepper. Stir in about 1/2 cup of the Gruyère and 1/2 cup of the Cheddar until melted and smooth. Taste and adjust seasoning.
  5. Arrange one-third of the sliced potatoes evenly in the prepared baking dish. Sprinkle lightly with salt and pepper, and dot with small pieces of the remaining 1 Tbsp of butter. Pour over one-third of the cheese sauce. Repeat this layering process two more times, ending with the sauce on top.
  6. Cover the dish tightly with foil. Bake for 45 minutes.
  7. Remove the foil. Sprinkle the remaining shredded cheese evenly over the top. Return to the oven (uncovered) and bake for another 15–25 minutes, or until the top is golden brown and a knife inserted meets no resistance.
  8. Let the dish rest on the counter for at least 15 minutes before slicing and serving.