Step 1

In a medium saucepan, melt butter and add flour, salt and pepper. Pour in the milk and bring to a boil. Stir frequently until thickened. Set aside.

Step 2

Lightly butter a large casserole (3.5 to 5 quart.). Preheat oven to 350 degrees F.

Step 3

Layer half of the sliced potatoes, 1/2 of the onion, 1/2 of the each cheese and sprinkle with salt and pepper. Pour 1/2 of the white sauce over the top. Repeat the next layer.

Step 4

Pour the remaining white sauce over the top, making sure you cover all. Sprinkle the final product with salt and pepper. Cover with foil and bake for 1 hour.

Step 5

Remove the cover and bake for another hour. Top will brown but not burn.