PREPARATION:

To make the chocolate base:

1. Whisk the milk and 1/3 cup/35 g of the cocoa powder in a heavy medium saucepan to blend.  Bring the chocolate milk to a simmer over medium heat, stirring occasionally.  Meanwhile, using a whisk, beat the egg yolks and 1/3 cup/65 g of sugar in a large bowl for 2 to 3 minutes, or until thick and light.
2. Whisk in the flour and cornstarch to blend.  Gradually pour the simmering chocolate milk over the egg yolk mixture, whisking until smooth.  Pour the chocolate custard back into the same saucepan.  Over medium-low heat, continually whisk the custard for 4 minutes, or until it thickens and bubbles just begin to burst through the top of the custard.
3. Transfer the custard to a clean mixing bowl.  Using an electric mixer, beat the custard on high speed for 6 to 8 minutes, or until it is thick and smooth and cools slightly. Cover the chocolate base with plastic wrap and refrigerate until cold.

To finish the Soufflés:

1. Preheat the oven to 375°F/160°C.  Coat six 6-ounce/170-ml soufflé dishes with butter and dust with cocoa powder to coat.  Using an electric mixer, beat the egg whites and remaining 1/4 cup/55 g of sugar in a large bowl just until medium stiff peaks form.  Fold one-third of the egg white mixture into the chocolate base (this will help lighten the base). Gently fold in the remaining egg white mixture.
2. Spoon the mixture into the prepared soufflé cups, dividing equally.  Place the soufflé dishes on a heavy large baking sheet and bake for  12 minutes or until soufflés have risen about 1 inch/ 2 1/2 cm above the dishes.  Dust the soufflés with powdered sugar and serve immediately.