For caramelized onions, cook onion in hot butter or margarine in a small saucepan, covered, over low heat about 15 minutes or until tender and golden, stirring occasionally. Meanwhile, stir together tomato preserves or mango chutney (cut up any large pieces of chutney), rosemary, and crushed red pepper in a small bowl.
Cut off a thin slice from the top of the Brie to remove the rind; discard. Place the Brie in an ungreased 9-inch pie plate. Top with tomato or chutney mixture, then with caramelized onions.
Bake, uncovered, in a 325 degree F oven about 10 to 12 minutes or until Brie is softened and warmed but not runny. Serve with breadsticks, crackers, or bread slices. Makes 8 servings.