Preheat and Prep:
Preheat oven to 320ºF (160ºC) for fan ovens or 338ºF (170ºC) for conventional. Line a baking tray with parchment paper.

Melt Chocolate and Butter:
Place chopped dark chocolate and butter in a heatproof bowl set over a pan of simmering water (don’t let the bowl touch the water). Stir gently until melted and smooth. Stir in the vanilla extract and set aside.

Beat the Eggs and Sugars:
In a separate large bowl, whisk the eggs, caster sugar, and demerara sugar on high speed until thick, pale, and fluffy—about 3–4 minutes.

Sift the Dry Ingredients:
In another bowl, sift together flour, cocoa powder, baking powder, salt, and optional chocolate chips.

Fold in the Chocolate:
Gently fold the melted chocolate mixture into the beaten eggs, being careful to preserve the volume.

Add the Dry Mix:
Fold in the dry ingredients until just combined—do not overmix.

Portion and Bake:
Drop heaping tablespoons of batter onto the prepared tray, spacing them out. Bake for 12–14 minutes, or until the tops are crackled and the edges are set.

Cool and Enjoy:
Let brookies cool on the tray for 10 minutes, then transfer to a wire rack to finish cooling. Optional: Sprinkle with flaky sea salt while warm for a sweet-savory twist.