Preheat the oven to 400°F (200°C). Generously grease and flour four 6-ounce ramekins.

In a heatproof bowl set over simmering water, melt the chocolate and butter together. Stir until smooth, then remove from heat.

In a separate bowl, whisk eggs, egg yolks, and sugar until pale and slightly thickened. Stir in vanilla and a pinch of salt.

Gently fold the melted chocolate mixture into the egg mixture. Sift in the flour and stir just until combined—avoid overmixing.

Divide the batter evenly among the prepared ramekins. Place them on a baking sheet.

Bake for 12–14 minutes, or until the edges are set but the centers still jiggle slightly.

Let cakes rest for 1 minute. Run a knife around the edges, invert onto serving plates, and dust with powdered sugar or cocoa.