1/4 cup chopped onion
1/4 cup butter
1/4 cup flour
2 1/2 cup milk
5 large potatoes (peeled & thinly sliced) (5 cups)
3/4 cup Cheddar cheese

Cook onion in butter until tender. Stir in flour, salt and pepper (to taste). Add milk and cheese. Cook until thick and bubbly. Cook and stir 1-2 minutes more.

Remove from heat. Place 1/2 of the potatoes in a greased 2 qt. casserole dish. Cover with 1/2 the sauce. Repeat layers.

Bake covered at 350°F for 45 minutes, stirring once. Uncover and bake for 30 minutes more--at this time sprinkle top with more cheese.