I just found this recipe while surfing the net.
Seems like a good decoration piece to add to things such as cakes.
Recipe source: adapted from chefkoch.de 
Prep time: 30 min., baking: 10-15 min.
(yields 2-3 baking trays):
|Ingredient||Weight||US Volume||Bakers Percentage|
|flour||150 g||5.29 oz||1.18 cups||100.00%|
|4 egg whites||80 g||2.82 oz||0.35 cups||53.33%|
|a pinch of salt||1 g||0.04 oz||0 tbspns||0.67%|
|white sugar||125 g||4.41 oz||0.62 cups||83.33%|
|2 tsp vanilla sugar*||10 g||0.35 oz||0.8 tbspns||6.67%|
|2 tbsp unsweetened cacao||10 g||0.35 oz||0.64 tbspns||6.67%|
|1/2 tsp cinnamon||3 g||0.11 oz||0.16 tbspns||2.00%|
Total Weight: 379 grams / 13.37 ounces
Total Flour Weight: 150 grams / 5.29 ounces
Bakers percentages are relative to flour weight (flour equals 100%) and every other ingredient is a percentage of this. Flour from the Starter is not counted. Note: This recipe was uploaded in grams and has been automatically converted to other measures, let us know  of any corrections.
* apparently if you cannot get vanilla sugar, it can be substituted directly for vanilla extract
Beat the egg whites in a large bowl together with a pinch of salt until they become very stiff (stiff enough to flip the bowl without making a mess).
Add sugar, vanilla sugar, cinnamon and cacao to the stiff egg whites, then blend in the flour until evenly combined.
Preheat the oven to 170°C (340°F). Cover your baking tray(s) with parchment paper or a silicon mat. Fill the batter in an icing bag and carefully pipe the alphabet or other shapes onto the tray. While the first attempts may look a little imperfect, you’ll become better with every new shape and letter. Be careful to leave enough space in-between, the cookies tend to rise a bit in size.
Bake on middle level for 10 to 15 minutes. The best way to find out if your cookies are done, is to take one out (they may still feel a little soft) and let it cool for 1 minute (they turn firm quickly and become crunchy). Remove them from the oven when done and let them rest on the trays for a few more minutes before picking them up. Store them in an airtight container as soon as they cooled down completely to keep them crunchy.