Preheat your oven to 425°F (220°C).
Grease 4 ramekins thoroughly with butter and dust them with cocoa powder to prevent sticking.
In a heatproof bowl, melt the butter and chocolate together. Microwave in 20-second intervals, stirring in between, until smooth and glossy.
In a separate bowl, whisk the eggs, egg yolks, and sugar until the mixture is pale and frothy.
Gently fold the melted chocolate mixture into the egg mixture until combined.
Sift in the flour and fold gently, being careful not to overmix.
Divide the batter evenly among the ramekins, filling each about three-quarters full.
Place the ramekins on a baking sheet and bake for 12–14 minutes. The edges should be set, but the center should still jiggle slightly when shaken.
Let the cakes cool for 1–2 minutes, then carefully invert them onto serving plates.
Serve immediately with your favorite toppings, like vanilla ice cream or fresh berries.