Preheat the oven to 350˚F (175˚C) and prepare two baking sheets with parchment paper.
Put the chopped chocolate and butter into a heat-proof bowl and place over the top of a simmering pot of water. Ensure the bottom of the bowl isn't touching the water. Heat and stir until all of the chocolate and butter is melted. Allow it to cool slightly while you begin making the cookies.
In the bowl of a stand mixer fitted with a paddle attachment, combine the brown sugar, white sugar, eggs, and vanilla, then beat until the mixture looks fluffy and has almost tripled in volume- 3 to 4 minutes on high.
Add the slightly cooled melted chocolate mixture to the stand mixer, then mix until well combined with the rest of the batter.
In a separate bowl, combine the flour, cocoa powder, baking powder, and table salt, then whisk until well combined. Then add this mixture to the stand mixer and beat on medium-low until just combined and smooth.
Using a 1 1/2-ounce (45 milliliter) cookie scoop, scoop the batter onto the two baking sheets (each sheet gets six cookies). The batter will be very thick and viscous- similar to brownie batter. It is best to work fast because the batter becomes hard to work with once it begins to cool.
Sprinkle the cookies with a little bit of flaky salt, then bake the cookies, one sheet at a time, for 12 minutes each.
Allow the cookies to cool completely before enjoying.