Place the dark chocolate and butter into a medium sized heat-proof bowl set over a saucepan of barely simmering water. Do not let the base of the bowl touch the water below. Heat, stirring often, on medium-low heat, until melted and smooth. Remove from the heat and set the bowl aside to cool. In a separate small mixing bowl, whisk together the all-purpose flour, coffee powder, baking powder, and salt. Set aside until needed. In the bowl of a stand mixer fitted with the whisk attachment, whisk the light brown sugar and eggs on medium speed, until thick, doubled in volume, and light caramel in color, about 4 minutes. Add in the melted and slightly cooled dark chocolate. Continue to whisk until well incorporated. Pause mixing to scrape down the bottom and sides of the bowl as needed. Set the mixer speed to medium-low and add in the dry flour ingredients. Whisk until just combined, then, add in the water. Continue to whisk until evenly incorporated. The dough should not be firm, but fluid, and leave a thick flowing “ribbon trail†when the whisk is lifted. Remove the bowl from the stand mixer and set it in the refrigerator to chill for at 15 minutes, or up to 30 minutes. Meanwhile, pre-heat the oven temperature to 180 Celsius (350 Fahrenheit). Line three large baking trays with non-stick parchment paper. Using a small cookie scoop, scoop the dough out and into evenly sized dough balls. The dough should be soft but will hold its shape when being scooped. If you are using a tablespoon to roll, the dough may become stickier and more difficult to work with. If this is the case, simply place the dough back in the refrigerator to slightly firm up before rolling. Make sure to space them an even distance apart, to allow room for spreading. You should fit about 8 to 10 balls per sheet. Tap the sheets three times against the kitchen bench, to slightly flatten and spread the cookies. Sprinkle over a little of the flaked salt. Bake the cookies, a sheet at a time, for about 11 minutes. 5 minutes into baking, open the oven-door and rotate the cookie sheet half-way around. Tap the sheet against the oven rack to flatten and crinkle the cookies. Close the oven door and allow the cookies to rise up again. 2 minutes later, open the oven door again, and tap the tray against the oven rack to again deflate and further crinkle the cookies. Once again, close the oven door, and allow them to rise up again. Another 2 minutes later, repeat this tapping process, for a final time. You’re aiming for cookies that are perfectly flat with plenty of crinkles. Allow the cookies to bake until done, about a further two minutes. They should be just firm around the edges and set in the middle. Remove from the oven and let the cookies cool on their trays for 10 minutes, before transferring to a wire rack to cool further before serving.