Pre-heat the oven to 180C / 170C fan.

Line 2 baking sheets with parchment paper or use a reusable baking mat

Cream together the butter and both sugars until light and slightly fluffy

Add the egg and vanilla extra, mixing it again

Add in the dry ingredients - flour, cocoa powder, bicarbonate of soda and salt. Beat until well combined then stir in the chocolate chips. The batter will be quite stodgy

Using a dessertspoon or cookie scoop, put cookie dough mounds onto the baking sheets, leaving a couple of inches between them to allow for spreading.

Bake for 10 to 12 minutes, or until the cookies have spread. The outsides will be drier and set, the insides will still be a little gooey.

Let the cookies cook on the baking sheets for 5 minutes, then transfer to a wire rack using a fish slice to cool completely (or eat when slightly warm).