In the top pan of a double boiler, combine the chocolate and butter. Set the pan over but not touching barely simmering water in the bottom pan and melt the chocolate and butter, then whisk until the mixture is glossy and smooth. Remove from the heat and stir in the vanilla and salt. Set aside to cool slightly.

In a large bowl, using an electric mixer, beat the egg yolks, 3 Tbs. of the sugar, and the cocoa powder on medium-high speed until thick. Spoon the chocolate mixture into the yolk mixture and beat until well blended. The mixture will be very thick.

In a bowl, using clean beaters, beat the egg whites on medium-high speed until they are very foamy and thick. Sprinkle in the remaining 3 Tbs. sugar and increase the speed to high. Continue beating until firm, glossy peaks form. Spoon half of the beaten whites onto the chocolate mixture and whisk in until just blended. Add the remaining whites and stir gently until just blended. Spoon into the prepared ramekins, dividing evenly.

Bake the cakes until they are puffed and the tops are cracked, 13 minutes. The inside of the cracks will look very wet. Remove from the oven and serve immediately in the ramekins. Or run the tip of a small knife around the inside of each ramekin to loosen the cake, then invert the cakes onto individual plates. Serve with a drizzle of crème anglaise.

Serves 6.