In medium skillet heat butter or margarine. Add onion, sweet pepper, raisins, and cloves. Cook and stir about 4 minutes or until onion is tender. Stir in vinegar and brown sugar; reduce heat. Simmer, uncovered, about 5 minutes or until liquid is nearly evaporated. Stir in walnuts. Remove from heat; cover and let stand for 10 minutes. Serve warm. Makes about 1 cup chutney.