01 - Preheat the oven to 425°F. Thoroughly butter four 6-ounce ramekins and lightly dust with flour, gently tapping out any excess.
02 - Combine the chopped chocolate and butter in a heatproof bowl. Place the bowl over a saucepan of simmering water, stirring continuously until the mixture is smooth and fully melted. Remove from heat and allow to cool slightly.
03 - In a separate mixing bowl, vigorously whisk together the eggs, egg yolks, powdered sugar, and vanilla extract until the mixture is thick and pale in color.
04 - Gently fold the cooled melted chocolate mixture into the whisked egg mixture until thoroughly combined and uniform.
05 - Sift in the all-purpose flour and a pinch of salt. Carefully fold the dry ingredients into the batter until just incorporated, being careful not to overmix.
06 - Evenly distribute the prepared batter among the four buttered and floured ramekins.
07 - Place the filled ramekins onto a baking sheet. Bake in the preheated oven for 11 to 12 minutes, or until the edges appear set but the centers remain soft and jiggly.
08 - Allow the cakes to cool in their ramekins for 1 minute. Carefully run a small knife around the edges of each cake, then invert onto individual serving plates. Serve immediately for best results.