Preheat oven to 220°C (425°F).
Prepare ramekins: Butter 4 ramekins thoroughly and dust with cocoa powder. Tap out excess.
Melt chocolate & butter: In a heatproof bowl, melt together over a double boiler or microwave in 20-second intervals. Stir until smooth.
Mix eggs & sugar: In a separate bowl, whisk eggs, egg yolks, and sugar until thick and pale.
Combine: Slowly fold the melted chocolate mixture into the egg mixture.
Add vanilla, salt, and gently fold in flour until just combined (do not overmix).
Fill ramekins: Divide batter evenly into prepared ramekins.
Bake for 10–12 minutes. The edges should be firm but the center soft.
Rest for 1 minute, then carefully invert onto plates.
Serve immediately while warm and molten inside.