01 - Preheat oven to 425°F. Generously butter four 6-ounce ramekins and dust with cocoa powder, tapping out the excess.
02 - Combine chopped dark chocolate and butter in a heatproof bowl set over barely simmering water, or microwave in short intervals. Stir until fully melted and smooth. Allow to cool slightly.
03 - In a medium bowl, whisk together eggs, egg yolks, granulated sugar, and vanilla extract until pale and slightly thickened, about 2 minutes.
04 - Slowly pour the cooled chocolate mixture into the egg mixture while whisking continuously until well combined.
05 - Sift in all-purpose flour and a pinch of salt. Gently fold with a spatula just until incorporated; avoid overmixing.
06 - Evenly divide the batter among prepared ramekins.
07 - Place ramekins on a baking tray and bake for 11 to 13 minutes, until the edges are set but centers remain soft and jiggly.
08 - Remove from oven and let rest for 1 minute. Run a small knife around each edge, invert onto a dessert plate, and lift off the ramekin.
09 - Serve immediately with optional powdered sugar, vanilla ice cream, or fresh berries.