Preheat your oven to 180°C (or 160°C for fan-forced). Line two baking trays with baking paper.

Melt dark chocolate and unsalted butter in a heatproof bowl over a double boiler until smooth. Let cool slightly.

In an electric mixer, beat eggs, caster sugar, soft light brown sugar, and vanilla extract for 5 minutes until pale and fluffy.

Slowly mix the melted chocolate and butter into the egg and sugar mixture until well combined.

Sift together plain flour, cocoa powder, baking powder, and salt. Gradually fold this dry mixture into the wet ingredients until just combined.

Portion the cookie dough onto lined baking trays, leaving space between each dollop.

Sprinkle flaked sea salt over each cookie and bake for 12 minutes until slightly underbaked in the center.

Let the cookies cool on the trays for at least 20 minutes before transferring to a wire rack.