Dip the potatoes in boiling water and cook for 20–25 minutes until almost ready.
In a skillet, melt butter over medium heat. Add flour and cook for a couple of minutes, stirring with a whisk. Pour in the milk and, while stirring, boil for 2–3 minutes until thick.
Remove the sauce from the heat, add salt, pepper and 200 g grated cheese. Stir to a smooth consistency.
Peel the cooled potatoes and cut into thin slices. Put a third of the potatoes in a greased form. Season with salt and pepper and pour over a slice of cheese sauce. In the same way, make two more layers. Sprinkle with the remaining grated cheese and bake for 20-25 minutes at 180 ° C.
