Blend the blanched almonds in a food processor fitted with a knife, or in a blender. They should be ground to a powder, but not too finely. Put the powdered almonds in the bowl of a food processor fitted with the sheet and add the sugars, cinnamon and flour.
Mix quickly, then add the egg whites and continue mixing until the dough forms a ball. Place the dough in cling film and chill for 2 hours.
Preheat oven to 150°C. Roll out the dough to a thickness of about 1 cm and cut out stars (or other shapes ^^) with a cookie cutter. Place the shortbread on a baking sheet covered with parchment paper and bake for 8 minutes. When removed from the oven, let cool completely.
For the glaze, beat the egg whites until stiff, then gently fold in the powdered sugar. Brush on the completely cooled stars and let dry for a few hours.
Notes
Storage: Once the icing is dry, you can store the cinnamon stars for several weeks in an airtight metal container.