Ingredients:

  • 3 lbs Russet or Yukon Gold potatoes, thinly sliced
  • 1 medium yellow onion, thinly sliced
  • 2 tbsp unsalted butter, melted
  • 1/2 tsp salt
  • 1/4 tsp black pepper
  • 3 tbsp unsalted butter
  • 3 tbsp all-purpose flour
  • 2 cups whole milk
  • 2 cloves garlic, minced
  • 2 cups sharp cheddar cheese, shredded
  • 1/2 tsp smoked paprika
  • 1/4 tsp ground nutmeg

Instructions:

  1. Grease a 9x13 inch baking dish with melted butter to prevent sticking.
  2. Use a mandoline to slice potatoes into 1/8-inch rounds and thinly slice the onion into half-moons.
  3. Toss the potato slices and onions in a large bowl with salt and pepper until evenly coated.
  4. Melt butter in a saucepan over medium heat, then whisk in flour and cook for 1–2 minutes until pale gold.
  5. Slowly pour in milk, whisking constantly, and simmer for 5 minutes until the sauce thickens.
  6. Remove the sauce from heat and stir in shredded cheese, garlic, paprika, and nutmeg until melted and velvety.
  7. Layer a third of the potato and onion mixture in the bottom of the dish, followed by a third of the cheese sauce.
  8. Repeat the layering process twice more, finishing with a final layer of sauce on top.
  9. Cover the dish tightly with foil and bake at 375°F (190°C) for 40 minutes.
  10. Remove the foil and bake for another 20 minutes until the top is bubbly and mahogany-colored.
  11. Let the dish rest for 10 minutes before serving to allow the sauce to set.