Scalloped Potatoes

6 medium potatoes, peeled and thinly sliced
4 tablespoons butter
3 tablespoons flour
1 teaspoon salt
1/4 teaspoon pepper
2 1/2 cups milk
1 small onion,diced finely

Preheat oven to 350ºF.

Heat 3 tablespoons of butter in a saucepan over low heat until melted. Blend in flour, salt and pepper. Cook over low heat, stirring constantly, until mixture is smooth and bubbly. Gradually stir in milk, 1/2 cup at a time. Heat to boiling. Boil and stir 1 minute.

Arrange potatoes in greased 2 quart casserole in 3 layers, topping each layer with part of the chopped onions and 1/3 of the sauce. Dot the top with the remaining 1 tablespoon of butter, broken into little pieces.

Cover and bake until potatoes are tender, about 90 minutes removing cover for the last 30 mins. Let stand 5 to 10 minute before serving. 

Serves 6