01 - Preheat oven to 425°F. Generously butter four 6 oz ramekins and lightly dust with flour, tapping out excess.
02 - Melt bittersweet chocolate and butter together in a heatproof bowl over simmering water, stirring until smooth. Remove from heat and allow to cool slightly.
03 - In a medium bowl, whisk eggs, egg yolks, and sugar until mixture becomes thick and pale, about 2 minutes.
04 - Gradually whisk the melted chocolate mixture into the egg mixture until fully incorporated.
05 - Sift in flour and salt, then gently fold the batter until just combined without deflating.
06 - Divide mixture evenly among the prepared ramekins.
07 - Place ramekins on a baking sheet and bake for 10 to 12 minutes until edges are set but centers remain soft and molten.
08 - Remove from oven and rest for 1 minute. Run a thin knife around edges to loosen, then carefully invert onto plates.
09 - Dust with powdered sugar and serve immediately, optionally garnished with fresh berries and a scoop of vanilla ice cream or whipped cream.