01 - Preheat oven to 425°F. Generously butter four 6 oz ramekins and dust with cocoa powder, tapping out the excess.
02 - Melt chocolate and butter together in a heatproof bowl over simmering water or in 30-second intervals in the microwave, stirring until smooth. Allow to cool slightly.
03 - Whisk whole eggs, egg yolks, and powdered sugar in a medium bowl until pale and thick, about 2 minutes.
04 - Stir melted chocolate and vanilla extract into the egg mixture until well combined.
05 - Sift in flour and salt, folding gently until just combined without overmixing.
06 - Divide batter evenly among prepared ramekins and place them on a baking sheet.
07 - Bake for 11 to 12 minutes, until edges are set but centers remain soft and slightly jiggly.
08 - Let cakes rest for 1 minute. Run a thin knife around edges and invert each cake onto a dessert plate.
09 - Serve immediately with vanilla bean ice cream. Garnish with berries or mint and dust with powdered sugar if desired.