Start by chopping the dark chocolate into small pieces for even melting. In a medium saucepan over low heat or in a microwave-safe bowl, combine the chocolate with the butter. Stir gently until smooth and glossy.

In a large mixing bowl, crack the two large eggs and add the demerara sugar and caster sugar. Whisk vigorously until pale and fluffy, about 3 to 5 minutes.

Once your chocolate mixture is melted and slightly cooled, slowly pour it into the egg-sugar mixture. Stir gently with a spatula to combine, aiming for a smooth, rich batter.

Sift together the plain flour and cocoa powder to remove lumps. Slowly add this dry mixture to the wet ingredients, folding gently with a spatula.

Gently fold in the chocolate chips if desired, ensuring they are evenly distributed throughout the batter.

Line a baking sheet with parchment paper and scoop rounded mounds of batter onto the sheet, leaving around 2 inches between each mound.

Preheat your oven to 350°F (175°C). When ready, place your baking sheet in the center rack and bake for 8 to 10 minutes until edges are set and centers look slightly soft.

Remove the sheet from the oven and let the brookies cool on the sheet for about 5 minutes before transferring to a wire rack to cool completely.