Line two baking trays with parchment paper and set them aside. Preheat the oven to 180C/350F.

In the bowl of a stand mixer or a large mixing bowl, cream together the butter and sugars until smooth and slightly paler in colour. Add in the vanilla and mix through. Sift the flour, coffee powder, cornflour, baking powder, bicarbonate of soda (baking soda) and salt into the mixing bowl. Beat together until the mixture resembles coarse wet delicious coffee flavoured sand.

Tip in the beaten egg and mix until just combined and the mixture is starting to form large clumps of cookie dough. Finally, add in the broken walnut pieces and gently fold through to disperse evenly.

Divide the mixture evenly into about a dozen cookie dough balls. You can do this using a cookie/ice cream scoop or by measuring out two tablespoons of dough for each cookie. If you prefer weighing the cookie dough, each ball will weigh about 50g. Gently press each cookie dough ball together just enough so it holds together. Place the cookie balls on the baking trays, allowing enough space for them to spread as they bake.

Pop the baking trays in the hot oven and bake for 9-10 minutes or until little cracks have made their way to the middle of the cookies. Remove from the oven and leave to cool on the baking tray. Enjoy!