Preheat the oven to 350°F (175°C).

In a saucepan, melt the butter over medium heat. Stir in the flour and cook for 1-2 minutes.

Gradually add the whole milk, whisking constantly until the mixture thickens.

Remove from heat and stir in 2 cups of shredded cheddar cheese, garlic powder, onion powder, salt, and black pepper until smooth.

Layer half of the sliced potatoes in a greased baking dish, then pour half of the cheese sauce over the potatoes.

Repeat with the remaining potatoes and cheese sauce.

Cover with aluminum foil and bake for 45 minutes.

Remove the foil, sprinkle the remaining cheddar cheese on top, and bake for an additional 15 minutes until the cheese is bubbly and golden.

Garnish with chopped parsley before serving.