Wash and peel the potatoes. Slice them thinly using a knife or slicer. Thin slices cook evenly and absorb the creamy sauce better. Keep slices similar in size for even baking.

In a saucepan, melt butter over medium heat. Add flour and whisk well. Slowly add milk while stirring. Cook until the sauce becomes thick and smooth. Add salt, pepper, and garlic powder for flavor.

Turn off the heat and mix in cheddar cheese. Stir until melted and creamy. This creates a rich cheese sauce. The sauce should be smooth and slightly thick for perfect layering.

Grease a baking dish lightly. Add a layer of potato slices. Pour some sauce over them. Repeat layers until all potatoes and sauce are used. Make sure every layer gets enough sauce.

Preheat oven to 180°C. Cover the dish with foil and bake for 40 minutes. Remove foil, sprinkle parmesan cheese and bake another 20 minutes. The top should be golden and bubbly.