In a small mixing bowl, whisk together the butter, sugar, cocoa powder, milk, and vanilla until smooth and combined.

Add the flour and fold in until combined.

Scoop out 0.5-oz dollops of the batter onto a lined baking tray and freeze whilst making the cookie dough.

Preheat the oven to 190C/375F/Gas 5, and line a baking tray with parchment paper or a silicone mat. Set aside.

In a medium mixing bowl, whisk together the flour, baking powder, baking soda, cornflour, and salt. Set aside.

In a separate large mixing bowl, whisk together the butter and sugars. Add the egg and vanilla, and whisk until combined.

Add the dry ingredients and mix until just combined. Fold in the chocolate chips.

Scoop the dough out into 2-oz balls. Flatten them out slightly, keeping the bottom thick.

Place a brownie batter ball into the centres.

Fold the cookie dough over the top, stretching the dough from the sides and pinching at the top, being sure to keep the dough at the bottom thick.

Place onto the prepared baking tray and freeze for 10 – 20 minutes until solid.

Once frozen, bake for 12 minutes.

Allow to cool on the baking tray for at least 10 – 20 minutes before transferring them to a wire rack to cool completely. The brownie centres will be very soft, but will firm up as they cool.