Heat dutch oven with butter and olive oil, add onions, salt, pepper, poultry seasoning, and bay leaf. Cook onions, stirring frequently until caramel colored(about 20 mins.) Add sherry to pot and deglaze. Add beef stock, cover pot and bring to boil. Remove bay leaf.
Toast bread and layer soup, bread and sprinkled cheese in 4 oven safe small soup bowls. Place under hot broiler on a cookie sheet until cheese melts and is bubbly.