# The Ingredients You'll Need:
→ Potatoes
01 - 3 pounds Yukon Gold or Russet potatoes, peeled and thinly sliced (about 1/8 inch)
→ Cheese Sauce
02 - 4 tablespoons unsalted butter
03 - 1 medium yellow onion, finely chopped
04 - 3 cloves garlic, minced
05 - 4 tablespoons all-purpose flour
06 - 2 1/2 cups whole milk, warmed
07 - 1 cup heavy cream
08 - 2 teaspoons Dijon mustard
09 - 1 teaspoon salt
10 - 1/2 teaspoon black pepper
11 - 1/2 teaspoon smoked paprika
12 - 2 cups sharp cheddar cheese, shredded
13 - 1 cup Gruyère cheese, shredded
→ Topping
14 - 1/2 cup shredded cheddar cheese
15 - 1/2 cup shredded Gruyère cheese
16 - 2 tablespoons chopped fresh chives (optional)
# Step-by-Step Instructions:
01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with butter or nonstick spray.
02 - Arrange half of the sliced potatoes in an even layer in the prepared dish.
03 - Melt butter in a large saucepan over medium heat. Add chopped onion and cook until softened, about 4 to 5 minutes. Add garlic and cook 1 more minute.
04 - Sprinkle flour into the saucepan and stir constantly for 1 to 2 minutes to form a roux.
05 - Gradually whisk in warm milk and cream, stirring until the mixture thickens, about 3 to 4 minutes.
06 - Stir in Dijon mustard, salt, black pepper, and smoked paprika.
07 - Remove sauce from heat and whisk in shredded cheddar and Gruyère until fully melted and smooth.
08 - Pour half the cheese sauce over the first potato layer. Add remaining potatoes, then top with remaining cheese sauce, spreading evenly.
09 - Cover dish with foil and bake for 45 minutes.
10 - Remove foil, sprinkle remaining cheddar and Gruyère cheese on top, then bake uncovered for 25 to 30 minutes until potatoes are tender and top is golden.
11 - Allow to rest for 15 minutes before serving. Garnish with fresh chives if desired.
