01 - Preheat oven to 425°F. Generously butter four 6 oz ramekins and lightly dust with flour, tapping out the excess.
02 - Set a heatproof bowl over a pot of gently simmering water. Add chocolate and butter, stirring constantly until completely smooth and melted. Remove from heat and let cool for 2-3 minutes.
03 - In a separate bowl, whisk together eggs, egg yolks, and powdered sugar until mixture becomes pale yellow and slightly thickened, about 2 minutes.
04 - Pour the warm chocolate mixture into the egg mixture along with vanilla extract. Whisk vigorously until fully combined and glossy.
05 - Sift flour and salt directly into the batter. Using a rubber spatula, gently fold until just incorporated. Take care not to overmix.
06 - Divide batter evenly among the prepared ramekins, filling each about three-quarters full.
07 - Place ramekins on a baking tray and bake for 11-12 minutes. The edges should be set while centers remain soft and slightly jiggly when gently shaken.
08 - Let cakes rest for 1 minute. Carefully run a thin knife around the edge of each ramekin, then invert onto serving plates. Wait 10 seconds before lifting off the ramekin. Dust with powdered sugar and serve immediately with fresh berries and ice cream if desired.