01 - Preheat your oven to 425°F. Generously butter four 6-ounce ramekins, then lightly dust the interiors with all-purpose flour, tapping out any excess.
02 - In a heatproof bowl set over a saucepan of simmering water (creating a double boiler), combine the chopped bittersweet chocolate and 1/2 cup unsalted butter. Stir continuously until the mixture is completely smooth and melted. Remove from heat and allow to cool slightly.
03 - In a separate mixing bowl, whisk together the large eggs, large egg yolks, powdered sugar, and vanilla extract until the mixture becomes thick, pale in color, and well combined.
04 - Gently fold the slightly cooled melted chocolate mixture into the whisked egg mixture until thoroughly combined and uniform in consistency.
05 - Sift the 1/4 cup all-purpose flour and a pinch of salt directly into the chocolate-egg batter. Carefully fold until the flour is just incorporated, taking care not to overmix.
06 - Divide the prepared batter evenly among the four buttered and floured ramekins.
07 - Place the filled ramekins onto a baking sheet. Bake for 11 to 12 minutes, or until the edges of the cakes are set and firm, but the centers remain soft and molten.
08 - Allow the baked lava cakes to cool in their ramekins for 1 minute. Carefully run a small knife around the inner edges of each ramekin, then invert each cake onto an individual serving plate. Serve warm without delay.