Heat remaining butter in skillet until it sizzles. Brown meatballs quickly over medium heat on all sides by shaking skillet. Transfer meatballs to ovenproof baking dish. Add a few tablespoons of milk to skillet; deglaze skillet stirring over medium heat; pour over meatballs. Bake about 15 minutes, or until meatballs are heated through.
Serve with mashed potatoes and sauce made from juices in the bottom of the casserole. (Blend with a little heavy cream over direct flame until slightly reduced to the consistency of thin sauce. Taste to correct seasonings.)