Preheat the oven to 180°C (without fan) and line a square baking pan with parchment paper.
Make the brownie batter: melt the Dark Chocolate with Butter until smooth, then whisk in the White Sugar and Brown Sugar until combined.
Stir in the Egg and Vanilla Extract until glossy, then fold in the Flour, Unsweetened Cocoa Powder and a pinch of Salt until just combined.
Make the cookie dough: cream together softened Butter with Brown Sugar and White Sugar until light, then beat in the Egg and Vanilla Extract.
Mix in the Flour, Baking Soda and a pinch of Salt until a soft dough forms, then stir in the Chocolate Chips.
Assemble the brookies by spreading the brownie batter evenly in the prepared pan, then drop spoonfuls of the cookie dough over the top and gently swirl with a knife or spatula to marble.
Bake at 180°C (without fan) for 25–30 minutes, or until the edges are set and the center is slightly soft.
Allow to cool in the pan before lifting out on the parchment and cutting into bars.
