01 -
Set oven to 160ºC (320ºF) fan or 170ºC (338ºF) conventional. Line a baking tray with parchment paper.
02 -
Combine chopped dark chocolate and butter in heatproof bowl over simmering water (not touching water). Stir until melted and smooth. Stir in vanilla.
03 -
Beat caster sugar, demerara sugar, and eggs with electric mixer until light, thick and fluffy.
04 -
Sift together flour, cocoa powder, baking powder, salt, and chocolate chips in separate bowl.
05 -
Fold melted chocolate mixture into whipped eggs, then gently fold in dry ingredients until just combined.
06 -
Scoop tablespoons of batter onto prepared tray, spacing well apart. Bake 12-14 minutes until set with crackly tops.
07 -
Sprinkle with sea salt if desired. Cool on tray 10 minutes, then transfer to cooling rack.