Preheat your oven to 160°C (320°F) for a fan oven or 170°C (338°F) for conventional. Line a baking tray with parchment paper.

Melt dark chocolate and butter in a heatproof bowl over simmering water. Stir until smooth, then remove from heat and add vanilla extract.

In a separate bowl, beat together room temperature eggs, demerara sugar, and caster sugar until light and fluffy, about 5 minutes.

Sift together plain flour, cocoa powder, baking powder, and salt in another bowl. Add chocolate chips and mix gently.

Fold the melted chocolate mixture into the whipped egg mixture gently, preserving airiness.

Add the dry ingredients to the wet mixture all at once. Gently fold until just combined.

Drop dollops of batter onto the baking tray, leaving space between each for spreading. Bake for 12-14 minutes until set.

Sprinkle sea salt over brookies while warm. Allow to cool on tray for 10 minutes, then transfer to a wire rack.