01 - Preheat oven to 425°F. Generously butter four 6-ounce ramekins and lightly dust with flour, shaking out excess.
02 - Melt chocolate and butter together in a heatproof bowl set over a saucepan of barely simmering water, stirring until smooth. Remove from heat and let cool slightly.
03 - In a separate bowl, whisk together eggs, egg yolks, sugar, and vanilla until pale and slightly thickened, about 2 minutes.
04 - Pour melted chocolate mixture into the egg mixture and whisk until fully combined.
05 - Sift in flour and salt, then gently fold until just incorporated.
06 - Divide batter evenly among the prepared ramekins.
07 - Place ramekins on a baking sheet and bake for 11-12 minutes, until edges are set but centers remain soft.
08 - Remove from oven and let rest for 1 minute. Run a thin knife around edges, then invert each cake onto a serving plate. Top with fresh berries and dust with powdered sugar. Serve immediately with whipped cream or ice cream if desired.