Step 1

Sift the flours and cocoa powder together. Set aside.

Step 2

Tip the butter into the bowl and whisk with a wooden spoon for a minute to lighten.

Step 3

Add the sugar and vanilla and whisk for another minute.

Step 4

Tip in the flour mix and work with the wooden spoon, then your fingers to form a dough.

Step 5

Lightly mix in the chocolate chips, if using. Don't knead the dough, use a light touch, and just your fingers, not the palm of your hand.

Step 6

Roll the dough out into logs, wrap in clingfilm and chill for 15 minutes in the fridge.Preheat the oven to 160˚C/310˚F.

Step 7

Take 1 log out of the fridge, and using a sharp knife, slice little discs about ½ an inch thick (just over 1 cm). Work quickly, as the dough warms up, it'll soften.

Step 8

Arrange the sliced dough on a baking sheet and bake for 15 minutes.Repeat with the other dough. Or, you can slice the other log, fill another baking tray and bake 2 baking trays at the same time. The tray on the lower shelf may need 2 minutes longer.Cool completely and store in an airtight container.