01 - Preheat your oven to 425°F. Grease four 6-oz ramekins with butter and lightly dust with flour, shaking out any excess.
02 - In a heatproof bowl set over a pot of simmering water (or in the microwave), melt the chocolate and butter together, stirring until smooth. Remove from heat and let cool slightly.
03 - In a mixing bowl, whisk together the eggs, egg yolks, and granulated sugar until pale and slightly thickened, about 2 minutes.
04 - Gently fold the melted chocolate mixture into the egg mixture.
05 - Sift in the flour, add vanilla extract and salt, and gently fold until just combined.
06 - Divide the batter evenly among the prepared ramekins.
07 - Place the ramekins on a baking sheet and bake for 10–12 minutes, until the edges are set but the centers are still soft (do not overbake).
08 - Let cakes cool for 1 minute, then carefully run a knife around the edges and invert onto dessert plates.
09 - Top each cake with a generous handful of fresh berries. Dust with powdered sugar and serve immediately, with whipped cream or vanilla ice cream if desired.