Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.

Melt the chopped dark chocolate and butter together in a microwave-safe bowl (30-second intervals) or over a double boiler. Stir until smooth. Let cool slightly.

In a large bowl, beat eggs, granulated sugar, and brown sugar on medium-high speed for exactly 5 minutes until pale and thick.

Pour the cooled chocolate mixture and vanilla into the egg mixture. Whisk on low until just combined.

Sift in the flour, cocoa powder, baking powder, and salt. Gently fold with a spatula until just a few flour streaks remain.

Fold in the chocolate chips until just combined. The batter will be loose.

Scoop batter onto prepared baking sheets using a medium cookie scoop, spacing 2 inches apart.

Bake for 10-12 minutes until tops are shiny and cracked. Do not overbake.

Remove from oven and immediately sprinkle with flaky sea salt. Allow to cool on the pan for 10 minutes before moving to a wire rack.