Preheat the oven to 150°C fan-forced / 170°C and line a baking tray with baking paper.
Place the butter, sugar, cocoa powder, flour, bicarbonate of soda and baking powder to the Thermomix bowl and mix for 30 sec/speed 4. Alternatively, use a food processor.
The dough will have come together and will be soft and easy to roll. If it's a little sticky, place in the fridge for 10-20 minutes to harden up.
Take out pieces about the size of a walnut then roll into a ball.
Place onto the baking tray, allowing plenty of space for them to spread.
Press each one down with a fork.
Bake in the oven for 15 minutes until they are just starting to harden around the edges.
The cookies will crack, and that's ok!
Leave them to cool on the baking tray 15 minutes then transfer them to a wire rack to cool completely.
The cookies will be soft when taken out of the oven but will harden once cooled.