Preheat the oven to 170°c/ Gas Mark 3. Grease or line a tray with parchment paper.

Sift the Plain Flour into a bowl. Add Bicarbonate of Soda and Salt and set aside.

Cream together the Butter, Brown sugar and Caster sugar until well blended.

Beat in the vanilla, egg and egg yolk until light and creamy.

Mix in the sifted ingredients until just blended.

Stir in the chocolate chips by hand using a wooden spoon.

Using your hands, roll the dough into Ping Pong size balls, placing them on the tray roughly 8cm apart. DO NOT FLATTEN THE DOUGH.

Bake for 15 minutes in the preheated oven, or until the edges are lightly toasted. Take them out before you think they're almost fully cooked.

Cool on baking trays for a few minutes before transferring to wire racks to cool completely.