1. Preheat the oven to 350°F (180°C). Line two baking sheets with baking parchment and set aside. Add the chopped chocolate and butter to a microwave-safe bowl and heat up slowly in the microwave until melted. Take out and let cool down again.

2. Add the eggs, both sugars, and the vanilla extract to a large bowl and mix on high until very light and fluffy – about 4-5 minutes. Add the melted (and cooled) chocolate to the bowl and mix until well combined. Mix the flour with cocoa powder, instant espresso powder, baking powder, and salt and add to the bowl – mix until just combined. Add the chocolate chips and fold in. Use a cookie scoop and place dough portions on the baking sheets with enough space in between. Sprinkle with some flaky sea salt and bake for 12-14 minutes. The cookies are done when the tops are firm with cracks all over. Take out of the oven, let cool down on the baking sheet for some time, then transfer to a wire rack and let cool down completely.