Preheat the oven to 425°F (220°C)
Grease 4 ramekins with butter
Dust the ramekins lightly with cocoa powder
Melt 1/2 cup butter and 4 oz semisweet chocolate together
Stir until smooth
Whisk 2 eggs, 2 egg yolks, 1/4 cup sugar, and a pinch of salt until thick
Fold the melted chocolate mixture into the egg mixture
Add 2 tablespoons flour and mix until just combined
Divide the batter evenly among the ramekins
Place the ramekins on a baking sheet
Bake for 10 to 12 minutes
Remove when the edges are set and the centers are soft
Let rest for 1 minute
Invert onto plates or serve in the ramekins
Serve immediately