3 pounds Yukon Gold or Russet potatoes, peeled and sliced into 1/8 inch rounds
1/4 cup unsalted butter
1/4 cup all purpose flour
2 cups whole milk
1/2 cup heavy cream
2 cups sharp cheddar cheese, shredded
1/2 cup Parmesan cheese, grated
1 teaspoon garlic powder
1/2 teaspoon onion powder
1 teaspoon salt
1/2 teaspoon black pepper
1/2 teaspoon fresh thyme leaves for garnish
Instructions
Preheat your oven to 375 degrees Fahrenheit and grease a 9 by 13 inch baking dish with butter or non stick spray. Peel your potatoes and slice them into thin, even rounds using a sharp knife or a mandoline slicer to ensure they cook at the same rate.
In a medium saucepan over medium heat, melt the butter until it begins to bubble. Whisk in the flour and cook for about one minute until the mixture is golden and smells slightly nutty, which helps remove the raw flour taste.
Slowly pour in the milk and heavy cream 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. Remove from heat and stir in the garlic powder, onion powder, salt, pepper, and one and a half cups of the cheddar cheese until smooth.
Arrange half of the potato slices in the bottom of the prepared baking dish in slightly overlapping rows. Pour half of the cheese sauce evenly over the potatoes. Repeat with the remaining potatoes and the rest of the sauce, ensuring all potatoes are well covered.
Cover the dish tightly with aluminum foil and bake for 45 minutes. Remove the foil, sprinkle the remaining cheddar and Parmesan cheese on top, and bake for another 15 to 20 minutes until the potatoes are tender and the top is golden and bubbly. Let the dish rest for 10 minutes before garnishing with fresh thyme and serving.
