Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper or silicone baking mats. Sift together the all-purpose flour, Dutch-process cocoa powder, baking powder, and fine sea salt in a small bowl; set aside.

In a heatproof bowl set over a small saucepan of gently simmering water (or in 20-second microwave bursts at 50% power), melt the chopped bittersweet chocolate and cubed butter together. Stir with a spatula until silky smooth and glossy. Remove from heat and keep warm.

In a large stand mixer fitted with the whisk attachment (or using a hand mixer on medium-high speed), vigorously beat the room-temperature eggs, granulated sugar, brown sugar, and vanilla extract for a full 4 to 5 minutes. The mixture must transform into a pale, thick, glossy foam that falls in ribbons.

With the mixer running on low speed, slowly stream in the warm melted chocolate-butter mixture. Gently fold until completely homogenous and glossy.

Add the sifted dry ingredients into the chocolate batter. Use a flexible rubber spatula to fold just until no flour streaks remain. Do not overmix. The batter will be glossy and similar to a thick, spoonable brownie batter.

Working quickly before the batter cools and sets, use a 2-tablespoon medium cookie scoop to drop mounds of batter onto prepared baking sheets, leaving 2 inches between each mound.

Bake at 350°F (175°C) for precisely 9 to 10 minutes. The cookies will puff up, develop shiny crinkled tops, and look slightly soft in the center. Do not overbake! Immediately upon removing from the oven, sprinkle generously with flaky Maldon sea salt and swirl a round cookie cutter or glass gently around each cookie to shape them into perfect circles. Let cool on the baking sheet for 10 minutes to set, then transfer to a wire rack or serve warm!