Preparation

• Preheat your oven to 160ºC (320ºF) with a fan or 170ºC (338ºF) for conventional heating and prepare a baking tray with parchment paper.
• In a heatproof bowl, combine the dark chocolate and butter. Place over a pan of simmering water and stir until melted and combined. Stir in vanilla extract.
• In a separate bowl, whisk the caster sugar, demerara sugar, and eggs with an electric whisk until light, thick, and fluffy (about 5 minutes).
• Sift together the flour, cocoa powder, baking powder, and salt in another bowl, then stir in the chocolate chips.
• Fold the melted chocolate mixture into the whipped eggs and sugars gently.
• Fold the dry ingredients into the wet mixture using a spatula until just combined.
• Scoop tablespoons of batter onto the prepared baking tray, allowing space for spreading. Bake for 12-14 minutes until set and crackly on top.
• Remove from oven, sprinkle with sea salt if desired, and let cool on the tray for about 10 minutes before transferring to a cooling rack.