In a medium saucepan over medium heat, melt butter, add flour and cook 2-3 minutes. Slowly stir in milk and cook until mixture thickens. Add garlic and salt and pepper to taste. Remove from heat.
3 Put a layer of half the potatoes in the dish and pour half the sauce on top. Repeat with the remainder of potatoes and sauce.
4 Bake covered 45 minutes. Uncover and bake about 15 minutes more until potatoes are tender and top is brown.