Caramelized Onion Marmalade

Melt butter in a large nonstick skillet over medium heat. Add sugar to pan; cook 1 minute or until sugar dissolves. Add onion and garlic to pan. Cover and cook 30 minutes or until onions are very tender, stirring occasionally. Uncover and add vinegar to onion mixture. Cook, uncovered, 10 minutes or until golden brown, stirring frequently. Stir in salt and pepper.