01 -
Preheat oven to 320°F with fan or 338°F for conventional heat. Line a baking tray with parchment paper.
02 -
Combine chopped dark chocolate and butter in a heatproof bowl. Place over a pan of simmering water, ensuring the bowl does not touch the water. Stir occasionally until fully melted and smooth. Stir in vanilla extract.
03 -
In a medium bowl, use an electric hand mixer on high speed to beat caster sugar, Demerara sugar, and eggs until the mixture is very light and thick, about 5 minutes.
04 -
Sift flour, cocoa powder, baking powder, and salt into a separate bowl. Add chocolate chips and mix to combine.
05 -
Gradually fold the melted chocolate and butter mixture into the whipped eggs and sugar mixture, stirring gently to maintain volume.
06 -
Carefully fold the dry ingredients into the wet ingredients with a spatula, mixing only until just combined to keep the batter light.
07 -
Scoop heaping tablespoons of batter onto the prepared tray, leaving space for spreading. Bake for 12 to 14 minutes, or until the tops are set and crackly.
08 -
Remove from oven and, if desired, sprinkle immediately with sea salt. Cool on the tray for about 10 minutes, then transfer to a wire rack to cool completely.