Preheat your oven to 425°F (220°C).
Grease four ramekins with butter and dust with cocoa powder.
Melt the butter and chocolate chips together in a microwave-safe bowl.
Stir until smooth and let it cool slightly.
In a separate bowl, whisk the eggs, egg yolks, and sugar until thick.
Add the melted chocolate mixture to the egg mixture and combine.
Gently fold in the flour and salt until just blended.
Pour the batter evenly into the prepared ramekins.
Bake for 12 minutes until the edges are firm but the center is soft.
Let the cakes cool for 1 minute, then invert onto plates and serve immediately.