1) Preheat oven to 375º. Melt butter in a sauce pot over low heat, whisk in flour and milk and cook until it thickens. Stir in chocolate and stir constantly until it's melted. Remove from heat and add coffee, vanilla, and half the sugar. One at a time, add the egg yolks while whisking constantly.
2) Butter a 2 to 2 ½ quart soufflé or baking dish.
3) In a perfectly clean and dry bowl , whisk the egg whites to soft peaks and gradually whisk in the remaining sugar and continue to whisk until the peaks stiffen. Gently fold the egg whites into the soufflé base and pour into the prepared baking dish.
4) Bake for 35 - 40 minutes until the soufflé rises 2 inches above soufflé dish. Dust with confectioners sugar and serve immediately because the soufflé will deflate in less than two minutes.