(Yields: 6 cups)
In a large stockpot, cook onions in butter until very soft, approximately 25 minutes. Reduce heat to low and add the flour, stirring until well blended. Cook on low heat, stirring frequently, for 20 minutes. Add the half & half and cream, and continue stirring. Add the mace and sherry, and simmer 45 minutes, stirring frequently. Add the crabmeat and simmer for 5 minutes. Ladle into soup bowls and serve immediately, topped with a splash of sherry. You must use good-quality crabmeat to obtain the desired quality of soup.