In a heatproof bowl set over gentle heat, melt the chopped dark chocolate and butter together, stirring until glossy and smooth.

Let the chocolate-butter blend cool slightly, then stir in the vanilla extract to infuse aroma.

In a separate bowl, whisk together eggs, caster sugar and demerara sugar until pale, thick and ribbon-like.

Sift flour, cocoa powder, baking powder and salt together in another bowl to eliminate lumps.

Gently fold the melted chocolate mixture into the whipped egg and sugar mixture, preserving airiness.

Add dry ingredients to the wet mix and fold until just combined, then stir in chocolate chips.

Drop spoonfuls of batter onto your prepared tray, spacing them apart so they don’t merge.

Bake until the tops crackle and edges set but centres remain soft, about 12–14 minutes.

Let cool on the tray briefly; they’ll firm up subtly as they rest.