Heat oil in a skillet and add the onions. Cook and toss until clear. Add thyme and bay leaves. Cook until the onions turn light brown. Add the chicken stock and simmer for 20 minutes. Add salt and pepper to the soup to taste. Pour into bowls, add croutons and top with cheese. Run under hot broiler until the cheese melts and begins to turn brown. (Hint: The better the cheese the better the soup. And the better cheeses are the ones that run over the side of the bowl and "crisp" up into a tasty treat all by itself.)