In a large skillet, sauté onion in 2 tablespoons margarine until golden. In large mixing bowl, beat egg; add milk and crumbs. Let stand 5 minutes. Add 1 1/4 teaspoons salt and next 5 ingredients and onions. Blend well with fork. In same skillet, heat 2 tablespoons margarine. Using 2 teaspoons, shape meat mixture into small balls about 1/2 to 3/4 inch in diameter. Drop some balls into skillet; brown well on all sides. Remove to warm casserole; repeat until all meat is browned, then into fat left in skillet. Stir flour and next 3 ingredients. Add water and cream slowly; stir until thickened. Gravy may be poured over meatballs in casserole or served separately.