1. 1. Preheat the oven to 425°F (220°C) and grease four ramekins with butter and cocoa powder.

2. 2. In a microwave-safe bowl, melt the butter and dark chocolate together in 30-second intervals until smooth.

3. 3. In a separate bowl, whisk the eggs, egg yolks, and sugar until light and fluffy. Stir in the melted chocolate mixture and vanilla extract.

4. 4. Gradually fold in the flour until just combined.

5. 5. Divide the batter evenly among the prepared ramekins.

6. 6. Bake for 12-14 minutes, or until the edges are set but the center is still soft and gooey.

7. 7. Let the cakes cool for 1 minute before carefully inverting them onto plates.

8. 8. Serve warm with a dusting of powdered sugar or a scoop of vanilla ice cream.