Step 1: Preheat your oven to 375°F (190°C). Grease a 9x13 inch baking dish with butter or non-stick spray.

Step 2: In a medium saucepan, melt the butter over medium heat. Stir in the flour, and cook for 1-2 minutes until the mixture is golden brown.

Step 3: Gradually whisk in the milk and cream, ensuring no lumps form. Cook, stirring constantly, until the sauce thickens, about 5 minutes.

Step 4: Remove the sauce from heat and stir in the garlic powder, onion powder, salt, pepper, and paprika.

Step 5: Arrange half of the sliced potatoes in the prepared baking dish. Pour half of the sauce over the potatoes and sprinkle with half of the cheese.

Step 6: Layer the remaining potatoes on top, followed by the remaining sauce and cheese.

Step 7: Cover the dish with aluminum foil and bake for 45 minutes. Remove the foil and bake for an additional 30 minutes until the potatoes are tender and the top is golden brown.

Step 8: Let the dish cool for a few minutes before serving. Garnish with chopped parsley if desired.