Grease four 6 oz ramekins with butter and dust with cocoa powder for easier release post-baking.

Place the ramekins on a baking sheet and preheat your oven to 425°F (220°C).

Melt the dark chocolate and unsalted butter together in a heatproof bowl using a double boiler or microwave. Stir until smooth and let cool slightly.

In another bowl, whisk together the whole eggs, egg yolks, and granulated sugar until the mixture is pale and slightly thick.

Slowly pour the warm chocolate mixture into the egg mixture, whisking gently to combine. Add a pinch of salt and vanilla extract if desired.

Sift the flour into the chocolate mixture and gently fold until just combined and smooth.

Pour the batter evenly into the prepared ramekins, filling them about ¾ full.

Bake for 10-12 minutes, until edges are set but centers remain soft.

Let the cakes sit for 1 minute after baking, then carefully loosen the sides with a knife and flip onto plates.

Serve warm with ice cream or a dusting of powdered sugar.