• Sift the cocoa powder into a bowl.
• Measure out three tablespoons of margarine and place them in a small saucepan. Melt the margarine.
• Add to cocoa powder and whisk well.
• Combine remaining margarine, sugar and vanilla sugar and, with a hand-held mixer, beat until foamy, for about 3 minutes.
• Add this mixture and the soy milk to the black cocoa mixture.
• Add flour, baking powder and salt.
• With your hands, knead the dough until smooth.
• Shape the dough into a disk and wrap in plastic.
• Refridgerate for 1 hour.
• Preheat the oven to 160°C.
• Roll out the dough between two layers of plastic wrap.
• It should be around 0.2 to 0.4 cm thick.
• Cut out cookies with a round cookie cutter (6 cm in diameter).
• Gather the remaining dough, roll it out, and cut out more cookies until there is no more dough to roll out.
• Place on a baking sheet lined with parchment paper.
• Bake for 7-9 minutes depending on the thickness.

To make the filling

• With a hand-held mixer beat the margarine for one minute.
• Add sugar and vanilla sugar in batches and beat until fluffy.
• Transfer to a piping bag with a large round tip and pipe on half the cookies.
• Press remaining cookies on top.