01 - Preheat the oven to 425°F. Grease four 6-ounce ramekins with butter and dust lightly with cocoa powder or flour, tapping out any excess.
02 - In a heatproof bowl set over a saucepan of simmering water, melt the chocolate and butter together. Stir until smooth and let cool slightly. Alternatively, microwave in 20-second bursts, stirring between each.
03 - In a separate bowl, whisk together the eggs, egg yolks, and sugar until pale and slightly thickened, about 2 minutes.
04 - Whisk the melted chocolate mixture and vanilla extract into the egg mixture until fully combined.
05 - Gently fold in the flour and salt just until no streaks remain. Take care not to overmix.
06 - Divide the batter 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. Tops should appear puffed and firm.
08 - Let rest for 1 minute. Run a knife around the edges and carefully invert each cake onto a serving plate. Serve immediately with vanilla ice cream. Dust with cocoa powder or powdered sugar and garnish with berries or mint if desired.