3 pounds Yukon Gold potatoes, peeled and sliced 1/8 inch thick
1/4 cup unsalted butter
1/4 cup all-purpose flour
3 cups whole milk, room temperature
1 teaspoon salt
1/2 teaspoon black pepper
1 teaspoon garlic powder
1 tablespoon fresh thyme leaves
1 cup shredded sharp white cheddar cheese
1/2 cup grated parmesan cheese
1/4 teaspoon ground nutmeg
Instructions
Preheat your oven to 375 degrees Fahrenheit and grease a 9 by 13 inch baking dish with butter. Wash, peel, and slice your potatoes into very thin, even rounds, about one eighth of an inch thick. Using a mandoline slicer is the best way to ensure they all cook at the same rate.
In a medium saucepan over medium heat, melt the butter. Once bubbly, whisk in the flour and cook for about one to two minutes until the mixture is golden and smells slightly nutty. This creates the base that will thicken your sauce perfectly.
Slowly pour in the milk while whisking constantly to prevent lumps from forming. Continue to cook and stir until the sauce thickens enough to coat the back of a spoon. Stir in the salt, pepper, garlic powder, nutmeg, and fresh thyme. Remove from heat and stir in half of the cheddar cheese until melted.
Arrange half of the potato slices in the prepared baking dish in overlapping rows. Pour half of the cheese sauce evenly over the potatoes. Repeat with the remaining potatoes and the rest of the sauce. Sprinkle the remaining cheddar and all of the parmesan cheese over the top.
Cover the dish tightly with aluminum foil and bake for 40 minutes. Remove the foil and bake for another 20 to 25 minutes, or until the potatoes are tender when pierced with a fork and the top is golden brown and bubbly. Let the dish rest for 10 minutes before serving to allow the sauce to set.
