For 4 servings
Preheat oven to 220°C (425°F). Grease four 6-oz ramekins with butter and dust with flour, tapping out excess.
Melt chocolate and butter together in a heatproof bowl set over simmering water, stirring until smooth. Remove from heat.
Whisk powdered sugar into the chocolate mixture until combined.
Add eggs, egg yolks, and vanilla; whisk until smooth.
Fold in flour and salt until just combined — do not overmix.
Divide batter evenly among prepared ramekins. Refrigerate up to 24 hours, or bake immediately.
Bake 10–12 minutes until edges are firm but center still jiggles slightly.
Let rest 1 minute, then run a knife around edges and invert onto plates. Serve with vanilla ice cream.