1/4 cup butter, 3 T. flour, 1 T. salt, Dash pepper, 3 cups milk, 5 large Yukon golden potatoes, peeled and thinly sliced.
In a large saucepan over medium heat, melt butter. Stir in the flour, salt and pepper until smooth. Gradually add milk. Bring to a boil; cook and stir for 2 minutes or until thickened and bubbly.
Place the potatoes in a greased 9" square baking dish. Add the sauce and stir gently to coat. Cover and bake at 325 degrees for 30 minutes. Uncover; bake 30 - 40 minutes longer or until the potatoes are tender.