Preheat the oven to 3750F (1900C). Grease a 9x13 inch baking dish.
In a saucepan, melt the butter over medium heat. Add the flour and stir to combine.
Gradually whisk in the milk until the mixture is smooth. Cook, stirring constantly, until the sauce thickens, about 5-7 minutes.
Add the grated cheddar cheese, salt, black pepper, garlic powder, and paprika to the sauce. Stir until the cheese is melted and the sauce is smooth.
Layer the sliced potatoes in the prepared baking dish. Pour the sauce over the potatoes, making sure to cover them completely.
Cover the baking dish with foil and bake for 45 minutes.
Remove the foil and bake for an additional 15-20 minutes, or until the potatoes are tender and the top is golden brown.
Let the scalloped potatoes cool for a few minutes before serving.
