Cream the butter and sugars

• Beat the softened butter with the brown sugar and granulated sugar until light and fluffy.
• Beat in the egg and vanilla extract until smooth.

Make the cookie dough

• Whisk together the flour, cocoa powder, baking soda and salt.
• Fold the dry ingredients into the wet mixture until just combined.
• Stir in the chocolate chips.

Shape the cookies

• Scoop the cookie dough into balls and flatten each one slightly in your palm.
• Place a spoonful of chilled brownie batter in the centre and wrap the cookie dough around it to seal.
• Set the filled balls on a lined baking tray, spacing them apart.

Chill the dough

• Chill the shaped cookies so they hold their shape while baking.

Bake

• Bake in a preheated oven at 180 °C until the edges are set and the centres are still soft.

Cool and serve

• Let the cookies rest on the tray, then transfer to a cooling rack.
• Serve slightly warm so the brownie centre is gooey.