Prep the ramekins. Heat the oven to 425°F (220°C).
Generously butter four 6-ounce ramekins, then dust with cocoa powder or sugar. Tap out the excess. This helps the cakes release cleanly.
Melt chocolate and butter. Place the chopped chocolate and butter in a heatproof bowl.
Set it over a pot of barely simmering water, stirring until smooth. You can also melt them in short bursts in the microwave, stirring between each burst.
Whisk the eggs and sugar. In a separate bowl, whisk the eggs, egg yolks, and sugar until slightly thick and pale, about 1 minute by hand. Stir in the vanilla and salt.
Combine wet and dry. Pour the melted chocolate mixture into the egg mixture and whisk to combine.
Sift in the flour and fold gently with a spatula until just blended. Do not overmix.
Fill the ramekins. Divide the batter evenly among the prepared ramekins. Place them on a baking sheet for easy handling.
Bake. Bake for 10–12 minutes.
The edges should look set, but the centers will still jiggle slightly. A light crust will form on top.
Rest briefly. Let the cakes sit for 1 minute. Run a thin knife around the edges to loosen.
Invert and serve. Place a dessert plate over each ramekin and flip carefully.
Lift the ramekin to release the cake. Serve immediately with ice cream, whipped cream, or a dusting of powdered sugar.