Preheat the Oven:

• Set the oven to 160ºC (320ºF) fan or 170ºC (338ºF) conventional.
• Line a baking tray with parchment paper.

Melt Chocolate and Butter:

• In a heatproof bowl, combine chopped dark chocolate and butter.
• Place the bowl over a pan of simmering water, ensuring it doesn’t touch the water.
• Stir occasionally until smooth, then mix in the vanilla extract.

Whip Eggs and Sugars:

• In a medium bowl, whisk eggs, caster sugar, and demerara sugar on high speed using an electric hand mixer.
• Whisk until the mixture becomes light, thick, and fluffy.

Combine Dry Ingredients:

• Sift together flour, cocoa powder, baking powder, chocolate chips, and salt in a separate bowl.
• This prevents lumps and ensures even mixing.

Integrate Chocolate Mixture:

• Gradually fold the melted chocolate and butter into the whipped eggs and sugars.
• Stir gently to retain airiness.

Fold in Dry Ingredients:

• Using a spatula, carefully fold the dry ingredients into the wet mixture.
• Mix only until just combined to maintain a light batter.

Bake the Brookies:

• Scoop tablespoons of batter onto the lined baking tray, spacing them apart.
• Bake in the preheated oven for 12-14 minutes, until set and crackly on top.

Cool and Finish:

• Remove from the oven and sprinkle with sea salt (optional).
• Let them cool on the tray for 10 minutes before transferring them to a cooling rack.