Peel and slice the onions into thin slices.
In a medium skillet add the butter, sliced onions and brown sugar and saute the onions until they become translucent and caramelized.
Add the cooked onions, beef broth, garlic, bay leaf and thyme to a 4 quart or larger crock-pot.
Cover and cook for 4 to 5 hours on LOW.
Add soup to ovenproof bowls and top with a slice or two of French bread.
Add both Swiss cheese and Parmesan cheese to top of bread.
Set the ovenproof bowls on a cookie sheet and place under the broiler for 1 to 2 minutes until the cheese is melted and bubbly.
Serve and enjoy!