01 -
Preheat oven to 320°F (160°C) with fan or 338°F (170°C) conventional. Line a baking tray with parchment paper.
02 -
Place chopped dark chocolate and butter in a heatproof bowl over simmering water, ensuring the bowl bottom does not touch the water. Stir occasionally until melted and smooth. Add vanilla extract and mix well.
03 -
Using an electric hand mixer on high speed, beat eggs with caster sugar and Demerara sugar until very light, thick, and fluffy, about 5 minutes.
04 -
Sift together flour, cocoa powder, baking powder, and salt into a bowl. Stir in chocolate chips evenly.
05 -
Gradually fold the melted chocolate and butter mixture into the whipped eggs and sugars, folding gently to preserve airiness.
06 -
Carefully fold the dry ingredients into the wet mixture using a spatula, mixing just until combined to maintain a light batter.
07 -
Spoon tablespoons of batter onto the prepared baking tray, spacing them to allow spreading. Bake for 12 to 14 minutes until set and crackly on top.
08 -
Remove from the oven, optionally sprinkle with sea salt immediately, then cool on the tray for 10 minutes before transferring to a wire rack to cool completely.