01 - Preheat oven to 425°F. Grease four 6-ounce ramekins generously with butter, dust with cocoa powder or flour, then tap out excess.
02 - Using a double boiler over barely simmering water, melt chopped dark chocolate with butter, stirring until smooth. Remove from heat and let cool slightly.
03 - In a separate bowl, whisk together eggs, egg yolks, and powdered sugar until thick, pale, and slightly foamy, about two minutes.
04 - Gradually whisk the melted chocolate mixture into the egg mixture until homogeneous. Add vanilla extract and salt, stirring gently.
05 - Sift flour over the batter and fold in carefully until just combined, taking care not to overmix.
06 - Divide the batter evenly among prepared ramekins, filling each about three-quarters full.
07 - Place ramekins on a baking sheet and bake for 11 to 13 minutes until edges are set but centers remain soft and slightly jiggly.
08 - Allow cakes to cool for one minute. Run a knife around edges, invert onto plates, remove ramekins carefully, dust with powdered sugar, and serve immediately with berries and vanilla ice cream if desired.