Whisk the egg whites until they form soft peaks, then trickle in the sugar, still beating, and continue beating for a further 10 minutes. Take about a third of the mixture and set aside covered with foil or clingfilm. Fold the cinnamon and ground almonds into the rest of the beaten egg whites. Sprinkle a work surface thinly with icing sugar and ground almonds and roll out the dough to a thickness of 1/2 cm. Cut out stars and spread with some of the reserved egg white mixture. Place on a baking tray lined with baking parchment and bake in a preheated oven (150°C, lower shelf) for about 10-12 minutes.