Melt the chocolate and butter together in a microwave-safe bowl, microwaving in 20-second intervals until smooth. Allow to cool to around 100°F.

In a separate bowl, whisk together the eggs, egg yolks, and granulated sugar until thickened and pale, about 2 minutes.

Fold the cooled chocolate mixture into the egg mixture, then sift in the flour and salt, mixing until just combined.

Cover the batter with plastic wrap and chill in the refrigerator for 30 minutes.

Preheat the oven to 425°F.

Butter six 6-ounce ramekins and dust the insides with cocoa powder.

Divide the batter evenly among the ramekins, filling each about 2/3 full.

Bake for 11 to 12 minutes. The edges should be firm, and the centers should jiggle slightly.

Let the cakes cool for 1 minute, then run a knife around the edges and invert onto plates to serve.