Preheat your oven to 425°F (218°C). Generously grease four 6-ounce ceramic ramekins with softened butter, then dust completely with cocoa powder, tapping out any excess.

Combine the chopped bittersweet chocolate and cubed butter in a heatproof glass bowl set over a saucepan of gently simmering water (or microwave in 25-second bursts), stirring until silky smooth. Remove from heat and cool for 4 minutes.

Whisk in the powdered sugar until thoroughly incorporated.

Add the whole eggs and egg yolks one by one, whisking thoroughly after each addition until thick and glossy. Stir in the pure vanilla extract and sea salt.

Gently fold in the all-purpose flour with a rubber spatula just until combined without overmixing. Divide batter evenly among the four prepared ramekins.

Place ramekins on a sturdy baking sheet and bake at 425°F (218°C) for exactly 12 to 14 minutes. The edges must be firm and slightly puffed, while the center remains soft with a gentle wobble.

Remove from the oven and rest for exactly 1 to 2 minutes. Run a small butter knife gently around the top edges, place an inverted dessert plate over each ramekin, and carefully invert. Rest for 10 seconds, then gently lift the ramekin.

Dust immediately with powdered sugar and serve warm alongside a scoop of vanilla bean ice cream.