For the marbled mocha cookies, mix all the ingredients together except the espresso powder. Divide the dough in half, and mix the espresso powder dissolved in a little hot water into one half of the dough.
Pour the dough alternately into a piping bag with a smooth nozzle and pipe small cookies onto a baking tray lined with baking paper.
Bake in the preheated oven at 160° hot air for about 13 minutes. Fill the marbled mocha cookies with any filling, for example jam.