In the bowl of your stand mixer, with the paddle attachment on, cream the softened butter with the powdered sugar for 2 minutes on medium low speed.
Mix in the egg white for about 1 minute until well incorporated.
Sprinkle the all-purpose flour and unsweetened cocoa powder. Continue to mix for another minute or until it is just combined. IMPORTANT: Do not over mix.
Place the dough in your Pastry Bag with the star tip on. Massage it for a minute in order to get the dough warmer. Then, pipe your spritz cookie into an "snail" shape.
BAKE!
Preheat oven to 350F/180C. Bake for 12 minutes (Every oven heats differently, monitor your butter cookies from 10min). It is ready when golden brown around the edge.
Once your Butter Cookies are out of the oven, let them cool down completely on your baking sheet. When ready, slide them onto a serving plate. Enjoy & Bon Appétit!