Preheat your oven to 160°C (320°F) for a fan oven or 170°C (338°F) for a conventional oven.

In a heatproof bowl, combine dark chocolate and butter over a pot of simmering water. Stir until melted, then add vanilla extract.

In another bowl, beat eggs with caster and demerara sugars for about 5 minutes until thick and fluffy.

Sift together flour, cocoa powder, baking powder, and salt. Fold in chocolate chips.

Gently fold melted chocolate mixture into egg and sugar mixture until smooth.

Add the dry ingredients to the wet mixture and fold until just incorporated, avoiding over-mixing.

Drop tablespoonfuls of batter onto a prepared baking tray, spacing them apart. Bake for 12-14 minutes.

Let brookies cool for about 5 minutes on the tray, then transfer to a wire rack to cool completely.