In the bowl of a stand mixer, cream the egg, brown sugar, peanut butter, butter and vanilla extract for about 5 minutes, or until light and fluffly.

Add the plain flour, baking soda, and salt to the mixing bowl and mix until just incorporated.

Break up your cooking chocolate into small pieces and fold into the cookie dough mixture using a spatula.

Cover your mixing bowl with cling-wrap and stick it in the fridge for at least two hours prior to baking.

After your dough chilled, preheat oven to 180C (350F), and line a baking tray with baking paper.

Remove your dough from the fridge, allow it to warm slightly, and use your hands to roll balls of cookie dough. Place on the tray with a few centimetres between each cookie (don't worry too much about shape, as the dough is chilled it should hold).

Bake cookies in oven for 8-10 minutes, until edges and top of cookies are just set. Remove from oven and allow to cool for an additional 10 minutes before serving.

Store in an airtight container for up to a week, if they last that long.