Preheat your oven to 200°C (390°F). Generously brush four ramekins with butter, then dust them with cocoa powder, tapping out the excess. This ensures easy release and adds a chocolatey crunch.
Gently melt the dark chocolate and butter together using a double boiler or microwave in short bursts, stirring until smooth and shiny. The aroma of rich chocolate will start to fill your kitchen.
In a separate bowl, whisk the eggs and superfine sugar until the mixture is pale, slightly thickened, and has a gentle froth—about 2 minutes. You'll notice the volume increase and a sweet aroma developing.
Pour the melted chocolate mixture into the eggs and sugar, folding gently with a spatula to combine. Add vanilla extract if using, and mix just until smooth—be careful not to deflate the mixture.
Sift the flour into the batter and fold gently to incorporate, maintaining a thick, glossy consistency. Overmixing can toughen the texture, so fold with care.
Divide the batter evenly among the prepared ramekins, filling each about three-quarters full. Smooth the tops with the back of a spoon for an even surface.
Place the ramekins on a baking tray and bake in the preheated oven for exactly 12-14 minutes. The edges should be set and firm, while the centers remain slightly jiggly when gently shaken.
Remove the ramekins from the oven and let them rest for about 1 minute. Carefully run a small knife around the edges to loosen, then invert onto serving plates with a gentle, confident flip.
Serve immediately while warm, with a dusting of cocoa powder or a scoop of vanilla ice cream. The crackly top and molten center will delight with each cut.
