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

In a heatproof bowl set over a small pan of simmering water (or in 20-second microwave bursts), melt the chopped bittersweet chocolate and butter together until glossy and smooth. Whisk in the instant espresso powder and set aside to cool slightly.

In a large bowl using an electric hand mixer with beaters, whip room-temperature eggs, granulated sugar, dark brown sugar, and vanilla extract on medium-high speed for a full 5 minutes until pale, frothy, and falling in ribbons.

Pour the warm melted chocolate mixture into the whipped egg mixture. Gently fold with a flexible silicone spatula until completely combined and glossy.

Sift in the all-purpose flour, Dutch cocoa powder, baking powder, and fine sea salt. Fold gently just until no dry flour streaks remain. Fold in the chocolate chips.

Immediately scoop batter using a 2-tablespoon cookie scoop onto the prepared baking sheets, spacing 2 inches apart.

Bake for 9 to 11 minutes at 350°F until edges are set, centers are soft, and tops are crinkled and shiny. Do not overbake!

Immediately out of the oven, gently swirl a round cookie cutter around each hot cookie to shape into a perfect round circle. Sprinkle generously with flaky Maldon sea salt. Let cool on the baking sheet for 10 minutes before serving.