Heat the oven to 425°F (220°C).

Grease small ramekins lightly with butter.

Melt the butter and chocolate together until smooth, then let it cool slightly.

Whisk in the powdered sugar until combined.

Add the eggs, egg yolks, and vanilla extract, then mix gently.

Fold in the flour and salt until just combined.

Divide the batter evenly among the ramekins.

Bake for 12 to 14 minutes until the edges are set and the centers remain soft.

Let the cakes rest briefly before serving warm.