Preparation

• Preheat your oven to 160ºC (320ºF) with a fan or 170ºC (338ºF) for conventional heating. Prepare a baking tray by lining it with parchment paper.
• In a heatproof bowl, combine the chopped dark chocolate and butter. Place this bowl over a pan of simmering water, stirring occasionally until fully melted. Stir in the vanilla extract.
• In a separate medium bowl, beat the caster sugar, demerara sugar, and eggs using an electric whisk until the mixture is light, thick, and fluffy, about 5 minutes.
• In another bowl, sift together the flour, cocoa powder, baking powder, and salt, then add the chocolate chips.
• Gradually fold the melted chocolate and butter mixture into the whipped eggs and sugars, stirring gently.
• Carefully fold the dry ingredients into the wet mixture using a spatula until just combined.
• Scoop tablespoons of batter onto the prepared baking tray, spacing them well apart. Bake for 12-14 minutes, until set and crackly on top.
• Remove from the oven and sprinkle with sea salt immediately. Let cool on the tray for about 10 minutes before transferring to a cooling rack.