Peel onions. Slice thinly.
In a large pot heat the oil and add the sliced onions. Caramelize -- this will take at least 30 to 45 mins. Be sure to keep an eye on to not scorch or burn the onions.
Once caramelized, season with salt and pepper. Add worchestershire, sherry and bay leaves. Add beef broth.
Simmer for about 1 hour.
Add croutons or chunks of baguette to the bottom of an oven proof bowl or onion soup bowl. Fill with soup. Cover with generous portion of cheese.
Broil for 1-2 min until cheese has melted. Serve.