This ultra-chocolatey cookie strikes the perfect balance between fudgy chew inside, and crisp crackle outside.
, at room temperature
PREHEAT oven to 350F and line 2 baking sheets with parchment.
WHISK eggs and sugar in the bowl of a stand mixer on medium-high until tripled in volume, 10 to 12 min. Whisk in vanilla.
MELT both chocolates and butter in a large heatproof bowl set over 1 in. of simmering water in a large pot, stirring until smooth, 2 to 3 min. Remove from heat.
WHISK flour, cocoa, salt and baking powder in a small bowl.
GENTLY fold one-third of egg mixture into the chocolate until no streaks remain. Fold in remaining egg mixture. Sift flour mixture over chocolate and gently fold until smooth.
SCOOP 1-tbsp portions onto prepared sheets, spaced 1 in. apart. Bake until cookies are puffy and cracked on top, 9 to 10 min. Sprinkle with sea salt and let cool on sheet for 2 min before transferring to a rack. Repeat with remaining batter.