Preheat the Oven
Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

Melt Chocolate and Butter
Place chopped chocolate and butter in a heat-proof bowl set over a pot of simmering water (double boiler method). Stir occasionally until melted and smooth. Set aside to cool slightly.

Whisk Dry Ingredients
In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt.

Beat Eggs and Sugar
In a large mixing bowl fitted with a whisk attachment, beat eggs, granulated sugar, light brown sugar, and vanilla extract on medium speed for 5 minutes, until pale and doubled in volume.

Combine Mixtures
Reduce speed to low and mix in the melted chocolate for 1 minute. Gently fold in the dry ingredients until just combined.

Add Chocolate Chips
Stir in the semisweet chocolate chips. The dough will resemble thick brownie batter.

Scoop and Shape
Use a medium cookie scoop (1½ tablespoons) to portion the dough onto baking sheets, spacing each cookie 2 inches apart.

Bake the Cookies
Bake for 12 to 14 minutes, rotating pans halfway through, until tops are shiny and crackly.

Cool and Finish
Remove from oven, sprinkle with flaky salt, and let cookies cool on the baking sheets for 10 minutes before transferring to a wire rack.