Put 1 cup (250 ml) of milk to boil with the sugar. Separately, dissolve the starch in 1 cup (250 ml) of milk. Put the sweetened milk in the starch mixture and put it to boil, while stirring it with a whisk. Remove from the heat, and while stirring continuously, add the 3 egg yolks that you've beaten with the coffee.
Separately, beat the egg whites with a pinch of salt into powdery snow and add them carefully to the cream. Pour the mixture into a glass cook pot or other suitable baking dish and then bake for a 1/2 hour in a moderate oven.
5-6 minutes before removing the coffee soufflé from the oven, sprinkle it with 1 tablespoon of sugar. Serve warm.