How to cook
Mix the eggs with natural cocoa powder, yoghurt, sugar, oil, baking soda and vanilla. Then, while beating constantly, slowly add the flour, until you get a dough (if needed, add more than 6 cups of flour).
Cover the dough with a towel for 15-20 minutes, then shape the dough into biscuits. Beat 1 egg yolk and smear each biscuit on top with the egg yolk. Sprinkle a little sugar on each biscuit if desired.
Put it to bake in the oven at 419°F (215 °C). Once baked, remove them and grate a little chocolate over each biscuit if desired.