Preheat the oven to 375°F (190°C). Grease a baking dish with butter.

Using a mandoline slicer or knife, thinly slice the potatoes and set aside.

In a saucepan, melt 3 tablespoons of butter over medium heat.

Whisk in the flour and cook for about 1 minute until bubbly.

Gradually whisk in the heavy cream and milk, stirring constantly until the mixture thickens.

Add 1 1/2 cups of cheddar cheese, garlic powder, onion powder, salt, and pepper. Stir until the cheese is melted.

Layer half of the sliced potatoes in the greased baking dish.

Pour half of the cream sauce over the potatoes.

Repeat with the remaining potatoes and sauce.

Sprinkle the remaining 1/2 cup of cheddar cheese on top.

Cover with aluminum foil and bake for 45 minutes.

Remove the foil and bake for an additional 15 minutes until golden and bubbly.

Let cool for a few minutes before serving.