Step 1

Put the flour, sugar, bicarbonate of soda, vanilla extract and margarine in a food processor and pulse until it looks like fine breadcrumbs. Add the egg and yolk and pulse until combined.

Step 2

Tip the dough onto a floured work surface and sprinkle over the chocolate chunks. Bring together with your hands, then divide into 20 balls.

Step 3

Heat the oven to 180ºC/350ºF/Gas Gently flatten each ball with the palm of your hand, then put on a baking tray lined with baking parchment – spread well apart (you may need 2 trays). Chill in the freezer for 10 mins, then bake for 8-10 mins.