1. In a large skillet or Dutch oven, saute onions in butter until tender and golden brown, about 25 minutes. Remove with a slotted spoon. Add flour, salt and pepper to skillet; stir until smooth. Gradually stir in milk until blended.
2. Bring to a boil; cook and stir for 2 minutes or until thickened. Reduce heat to medium. Return onions to the pan; heat through.