For the dough: In a large bowl, beat the egg whites until stiff, then sprinkle in the sugar and continue to beat until the meringue is stiff and glossy. Add the ground almonds, hazelnuts, gingerbread spice and rum extract. Knead the dough, cover, then store for about 1 hour in the refrigerator.
Sprinkle a little sugar on a work surface.
Roll out the dough to about 5 mm (about 0.5 cm) thick. Cut out cresent moons and place on a baking tray with parchment paper. Allow the cookies to sit for about 2 hours.
Preheat the oven to 175°C (approximately 350°F) and bake for 6-8 minutes. Remove and let cool.
For the icing: Mix together the powdered sugar, rum and a little water until icing is spreadable.
Glaze the cookies and sprinkle with chocolate sprinkles.
Let the icing dry completely before storing the cookies.