Ingredients:

  • 3 pounds Yukon Gold potatoes, peeled
  • 1 large onion, thinly sliced (about 1 cup)
  • 2 cloves garlic, minced (about 2 teaspoons)
  • 4 tablespoons unsalted butter
  • 4 tablespoons all-purpose flour
  • 3 cups whole milk
  • 1/2 teaspoon ground nutmeg
  • Salt and freshly ground black pepper to taste
  • 1 1/2 cups shredded sharp cheddar cheese
  • 1/2 cup shredded Gruyere cheese
  • 1/4 cup grated Parmesan cheese (for topping)

Instructions:

  1. Preheat oven to 375°F (190°C). Grease a 9x13 inch baking dish. Slice the potatoes thinly (about 1/8 inch thick) using a mandoline or sharp knife. Layer in the baking dish. Sautee the sliced onion and garlic until fragrant.
  2. Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1-2 minutes to make a roux. Gradually whisk in milk until smooth. Bring to a simmer, stirring constantly, and cook until thickened (about 5-7 minutes). Remove from heat and stir in nutmeg, salt, and pepper. Season to taste.
  3. Pour half of the cream sauce over the potato layers. Sprinkle with half of the cheddar and Gruyere cheese. Repeat layers with remaining potatoes, sauce, and cheese.
  4. Sprinkle the top with Parmesan cheese. Bake for 50-60 minutes, or until the potatoes are tender and the top is golden brown and bubbly. Let stand for 10 minutes before serving. A knife inserted into the centre potatoes should meet little to no resistance.