In a large saucepan, melt the butter and saute the onion gently until it's soft but not brown. Add the potatoes, sugar, stock, and sprouts. Bring to a boil, lower the heat, cover and simmer for about 15 minutes, until the vegetables are soft. Turn off the heat.
Puree the soup in a blender and return it to the saucepan. Stir in the cream, ham and sherry, and season to taste. To serve hot, reheat gently (don't let it boil); to serve cold, cover and refrigerate for a few hours before serving.
From the Dinner Co-op