In a large non-stick pan, cook onions, butter and brown sugar over medium low heat until golden and caramelized. (About 20 minutes).Once golden, add to the slow cooker along with remaining ingredients except bread and cheeses.Cook on low for 6-8 hours.Remove and discard bay leaf and ladle the soup into bowls. Top with dry bread slices and cheeses. Broil 2-3 minutes or until cheese is melted and browned.