1. Add about 9 oz. (250g) of the chopped chocolate together with the butter to a heatproof bowl over a pot with simmering water and melt (also works in the microwave). Mix until combined and set aside to cool down again.

2. Add the eggs and brown sugar to a large bowl and mix until light and fluffy. Add the melted chocolate and vanilla extract and mix until well combined. Mix the flour with baking powder, salt and espresso powder. Add to the bowl and mix until just combined. Fold in the remaining chopped chocolate. Place the dough in the fridge for about 20 minutes.

3. Preheat the oven to 180°C (350°F). Line a baking sheet with baking parchment. Use a spoon or cookie scoop* to place dough balls on the baking sheet – leave enough space in between. Sprinkle the dough balls with some flaky sea salt and bake for about 7-8 minutes. The edges of the cookies should get some color and the top some cracks. Do not overbake the cookies. Take them out of the oven, let them cool down a bit on the baking sheet, then let them cool down completely on a wire rack. Do the same with the remaining dough.