In a stand mixer, beat together butter and sugars until pale and creamy.
Add egg and vanilla paste and beat for a further two minutes to combine.
Add flour and cocoa powder, half the amount each time, alternating between the two. Stir in using a spatula.
Chop ginger and walnuts into approximately 0.5 centimetre cubes. Add to cookie dough and stir to combine.
Using an ice cream scoop, scoop balls of dough (around 45-50g each), roll into a ball and place on to prepared baking tray. Press down with your fingers to flatten dough into cookies.
Bake for 12 minutes. Remove from the oven and allow to cool on the tray for five minutes before placing on a cooling rack.