Method

• 1.
  Preheat oven to 180°C/160°C fan-forced. Line 2 large baking trays with baking paper.
• 2.
  Place butter and dark (40%) chocolate in a medium heatproof bowl set over a small saucepan of simmering water over medium heat (don’t let base of bowl touch the water). Stir constantly until melted and smooth. Remove bowl from pan and set aside.
• 3.
  Meanwhile, sift flour, cocoa powder and baking powder into a medium bowl, then stir through 1/2 tsp salt flakes.
• 4.
  In a stand mixer fitted with the whisk attachment, whisk eggs and both sugars on medium-high speed for 3 minutes, or until very thick and pale. Add one-third of the melted chocolate mixture and whisk gently on low speed until just combined, then add remaining melted chocolate mixture and whisk on low speed until just combined.
• 5.
  Add sifted flour mixture to egg mixture and fold together until just combined (do not overmix). Working quickly, spoon slightly heaped ⅓-cup measures of mixture onto the prepared trays in mounds, leaving plenty of space in between each mound to allow for spreading, to create 8 cookies in total (4 per tray). No need to press down; they will spread during cooking.
• 6.
  Bake trays, one at a time and on the middle shelf in the oven, for 13-15 minutes, until edges have crackled and centres are slightly soft. Remove from oven and carefully and lightly press squares and chopped pieces of dark (70%) chocolate into tops of each hot cookie, then sprinkle lightly with salt flakes. Cool on trays for 30 minutes, then transfer to a wire rack to cool completely before serving (or see recipe notes).