1. Preheat the Oven
Preheat your oven to 160ºC (320ºF) with a fan or 170ºC (338ºF) for conventional heating. Line a baking tray with parchment paper to prevent sticking.

2. Melt Chocolate and Butter
In a heatproof bowl, combine the chopped dark chocolate and butter. Place the bowl over a pan of simmering water, ensuring the bowl doesn’t touch the water. Stir occasionally until the chocolate and butter are melted and fully combined. Set aside to cool slightly.

3. Whip Eggs and Sugars
In a separate medium bowl, use an electric hand whisk to beat the caster sugar, demerara sugar, and eggs together on high speed. Whip the mixture until it becomes pale, thick, and fluffy. This process will incorporate air, giving the brookies their signature crackly top.

4. Combine Dry Ingredients
In another bowl, sift together the flour, cocoa powder, baking powder, and salt. Sifting helps remove lumps and ensures that the dry ingredients are evenly distributed.

5. Integrate the Chocolate Mixture
Once the melted chocolate and butter have cooled slightly, gradually fold it into the whipped eggs and sugar mixture. Stir gently to maintain the lightness and airiness of the whipped eggs.

6. Fold in Dry Ingredients
Using a spatula, carefully fold the dry ingredients into the wet mixture. Be gentle to avoid deflating the batter—mix just until combined.

7. Add Chocolate Chips
Fold in the dark or milk chocolate chips, ensuring they’re evenly distributed throughout the batter.

8. Bake the Brookies
Scoop tablespoons of the batter onto the prepared baking tray, spacing them apart to allow for spreading. Bake in the preheated oven for 12-14 minutes. The brookies should have a set, crackly top but remain soft in the center.

9. Cool and Finish
Remove the brookies from the oven and, if desired, sprinkle a pinch of sea salt on top while they’re still warm. Let them cool on the baking tray for 10 minutes before transferring to a cooling rack to cool completely.