This delicious warming drink is especially good at Christmas. In a basin, beat together the egg yolks, egg whites, sherry and spices. Pour into a large saucepan and heat gently, stirring all the time until warm, but not thick. Heat the cream and most of the sugar in another saucepan and as they come to the boil, pour from a good height into the warm egg mixture. Allow to stand for a few minutes in a warm place, then sprinkle the reserved sugar over the surface, and serve in warm wine glasses or pottery goblets.