Heat the chocolate, cornflour, cocoa powder and coffee granules with 1 tablespoon of the sugar and the milk in a pan over a low heat until the chocolate has melted. Continue heating, stirring all the time until the chocolate mixture thickens. Remove from the heat and cool slightly, then stir in the egg yolks and cover with a piece of nonstick baking paper.
Whisk all the egg whites in a grease-free bowl until softly peaking. Gradually whisk in the rest of the sugar until the eggs are stiffly peaking. Fold one-third of the egg whites into the chocolate mixture, then fold in the rest of the egg whites.
Grease 6 heatproof cups or ramekins, each 150 ml (¼ pint), and spoon in the chocolate soufflé mixture. Bake in a preheated oven, 190°C (375°F), Gas Mark 5, on a hot baking sheet for 12 minutes or until the soufflés are puffed up.
Dust with cocoa powder and eat immediately.