Preheat oven to 425°F (220°C). Grease 4 ramekins (6 oz each) with 1 tbsp softened butter and dust with 1 tbsp cocoa powder; tap out excess. Melt the 4 oz bittersweet chocolate and 4 tbsp unsalted butter together in a heatproof bowl over barely simmering water, stirring until smooth, about 3 to 4 minutes. Remove from heat.

In a medium bowl, whisk the 2 large eggs, 2 large egg yolks, and 3 tbsp granulated sugar vigorously for 2 minutes until pale and slightly thickened. Whisk in the 1 tsp vanilla extract.

Fold the warm chocolate mixture into the egg mixture with a rubber spatula until just combined. Sift in the 2 tbsp flour and 1 pinch fine salt and fold until no dry streaks remain.

Divide the batter evenly among the prepared ramekins. Place on a baking sheet and bake at 425°F (220°C) for 12 to 13 minutes, until edges are set and the center has a slight jiggle.

Run a thin knife around the edge of each ramekin, invert onto a dessert plate, hold for 5 seconds, and lift the ramekin away. Add a scoop of vanilla ice cream alongside and serve immediately.