Preheat oven to 380°

Scalp potatoes skins. Rinse. Cut potatoes in half. Then cut into 1/8 in. slices and halve if necessary.

Remove onion skin. Cut onion in half. Dice onion.

In sauce pan, mix in butter, flour, milk, salt, and black pepper. Add additional milk if too thick. Add butter and flour if too thin.

In casserole dish, grease inside with nonstick spray. Afterwards, add all ingredients together in a layered formation.

Bake for 60 mins at 380°