Over medium heat, combine olive oil and butter and heat until butter is melted. Add all the sliced onion and stir well. Season with sea salt, cover, and cook until onions are reduced, soft and translucent. This is an important step because you do not want firm onions when you serve your soup.
Add the sherry or wine to the cooked onions and simmer for 2 minutes.
Add the stock and the bay leaves and simmer for 25 minutes.
Toast the sliced French bread, then rub the raw clove of garlic a few times across the French bread.
Place each slice of French bread on a baking sheet, add the desired amount of shredded cheese on top of French bread and broil until the cheese is melted. About 1-2 minutes.
Ladle the soup into serving bowls and top each bowl with a slice or two of toasted melted cheese bread.
Garnish with chopped parsley or green onion tops.