Add sugar and cocoa powder, and mix everything together.
Add ground cinnamon. Split the vanilla pod lengthwise, scrape out the seeds, and add to the mixture. Finely grate fresh ginger over the mixture.
Add the egg, cold butter (cut into small pieces), and water.
Mix until smooth using a hand mixer, or work manually by mixing with a wooden spoon and crushing the butter pieces repeatedly. Then place on a worktop and knead until smooth. Add a little more water if the dough is too stiff.
Add chili powder or hot sauce a few drops at a time, kneading well after each addition. Taste the dough and continue adding chili until you reach your desired heat level. Remember that the fat in the dough will dull the spiciness, so use considerably more chili than you might initially expect.
Shape the dough into a ball, wrap tightly in plastic wrap, and refrigerate for at least a few hours or preferably overnight.
Preheat the oven to 180°C (356°F).
Remove the dough from the refrigerator, knead until smooth, and roll out to approximately 5 mm thick. Rolling under plastic wrap works well to prevent sticking.
Cut out tree shapes and place them on a baking sheet lined with parchment paper.
Bake on the middle rack at 180°C (356°F) for about 10 minutes.