Preheat oven 350 degres. Greased a 1.5 liter (8 by 8 or 9 by 9 inch) baking tray.
In saucepan, melt butter allso stir in flour.
beat in milk and season with salt & hot pepper.
Simmer the sauce over low heat until smooth and boiling, stirring occasionally with an electric beater.Reduce heat & stirring in one c of cheddar cheese.
Putting half of diced potato in baking dish. Pour half of cheese sauce on potatoes. Repeat with second layer of potatoes & cheese sauce