Measure milk into a 2-quart saucepan. Add potatoes, salt, pepper, and butter. Bring to a boil, reduce heat and simmer until almost tender, about 6 minutes. Remove from heat, add cheese, and stir carefully until just melted. Sprinkle flour over the surface, stir gently then pour into a greased 2-quart casserole. Bake at 400° for 20 minutes, until browned.
Au gratin potato recipe serves 6.