How to Make It
Heat 1 tablespoon butter in a skillet over medium. Add onions; cook 20 minutes, stirring occasionally. Add sugar; cook 2 minutes. Stir in vinegar. Cover, reduce heat, and cook 25 minutes, adding up to 1/4 cup water, 1 tablespoon at a time, if pan seems dry. Stir in remaining 1 1/2 teaspoons butter, salt, and pepper. Top with parsley.