01 - Preheat oven to 425°F. Generously butter four 6 oz ramekins and dust with cocoa powder, tapping out any excess.
02 - Combine chopped chocolate and butter in a heatproof bowl over simmering water. Stir until smooth and remove from heat to cool slightly.
03 - In a separate bowl, whisk eggs, egg yolks, and vanilla extract until thick and pale.
04 - Sift powdered sugar, flour, and sea salt into the egg mixture. Fold gently to combine.
05 - Fold the melted chocolate mixture into the batter until just combined without overmixing.
06 - Divide batter evenly among prepared ramekins.
07 - Bake for 11 to 12 minutes, until edges are set but centers remain soft.
08 - Let cakes rest for 1 minute, then invert onto plates. Serve immediately, optionally with vanilla ice cream or powdered sugar.