Whip the margarine previously kept at room temperature until fluffy and smooth (2-3 minutes).

Sieve into the icing sugar a bit at a time mixing all the time with an electric whisk.

Also add vanilla extract and sifted flour, a spoonful at a time. 

Transfer half of the mixtrure into a piping bag making sure it stays to a side.

Add cocoa powder to the remaining dough and incorporate it into the mixture gently.

Transfer the cocoa mixure to the other side of the piping bag and push both doughs down to the cap.

Pipe 16 round circles of dough onto a tray covered in baking sheet. Put the tray in the refrigerator for at least half an hour.

Preheat the oven at 180°C (356°F) and bake the cookies for 10-12 minutes. Allow the cookies to cool completely before eating.