01 - Preheat oven to 425°F. Generously butter four 6-ounce ramekins and dust with cocoa powder or flour, tapping out excess.
02 - Using a double boiler, melt dark chocolate and butter together, stirring until smooth. Remove from heat and allow to cool slightly.
03 - Whisk eggs, egg yolks, and powdered sugar in a separate bowl until thick, pale, and foamy, approximately 2 minutes.
04 - Gently whisk the melted chocolate mixture into the egg mixture until combined. Add vanilla extract and salt.
05 - Sift flour over the batter and fold in gently until just blended; avoid overmixing to maintain texture.
06 - Divide batter evenly among prepared ramekins, filling each approximately 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 - Let cakes cool for 1 minute, then run a knife around the edges, invert onto serving plates, and remove ramekins.
09 - Dust with powdered sugar and serve immediately with fresh berries and vanilla ice cream, if desired.