Preheat oven to 350?F and line two baking sheets with parchment paper.

Whisk together flour, cocoa, baking powder, and salt in a medium bowl.

Melt chopped chocolate and butter in a double boiler or heat-proof bowl over simmering water until smooth, then remove from heat to cool slightly.

In a large mixing bowl, whisk together eggs, granulated sugar, brown sugar, and vanilla at medium speed for 5 minutes until pale and fluffy.

Reduce mixer speed to low, and beat in melted chocolate for 1 minute.

Add the flour mixture and mix on low speed for 20 seconds, until just combined.

Gently fold in chocolate chips.

Use a medium cookie scoop to form cookies, placing them 2 inches apart on the lined baking sheets.

Bake for 12 to 14 minutes, rotating pans halfway through. The tops should look shiny and crackly.

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