Cover the sultanas with cold water and set aside to plump up. Cover the potatoes with cold water and cook until soft. Peel them and mash in a pan. Add the butter, cream, salt and flour and mix together over low heat. Add the sugar, spices and egg yolks and mix very thoroughly, then turn the mixture into a bowl.
Whisk the egg whites until stiff, then fold them into the mixture. Squeeze o