Preheat your oven to 160ºC (320ºF) with a fan, or 170ºC (338ºF) for conventional ovens. Line a baking tray with parchment paper and set aside.

In a heatproof bowl, combine chopped dark chocolate and butter. Place the bowl over a saucepan of simmering water (make sure the bowl doesn't touch the water). Stir until the mixture is completely melted and glossy. Stir in the vanilla extract and set aside to cool slightly.

In another bowl, beat the eggs, caster sugar, and demerara sugar using an electric hand mixer on high speed for about 5 minutes. You’re looking for a pale, thick, and airy mixture—this helps give the brookies their signature crackly top.

In a separate bowl, sift together the flour, cocoa powder, baking powder, and salt. Stir in the chocolate chips. Sifting helps avoid clumps and distributes the ingredients evenly.

Gently fold the melted chocolate mixture into the whipped egg and sugar mix. Be careful to preserve the fluffiness. Then fold in the dry ingredients just until combined. The batter will be thick and glossy—resist the urge to overmix.

Drop tablespoons of batter onto the prepared baking sheet, spacing them about 2 inches apart. Bake for 12–14 minutes, or until the tops are crackly and the edges look set but the centers are still soft.

Let the brookies cool on the tray for 10 minutes, then transfer to a wire rack. Optional but highly recommended: sprinkle with a pinch of sea salt for that sweet-salty finish.