Position rack in center of oven and preheat to 450°F.
Butter a 1-quart soufflé dish and sprinkle with sugar.
Melt butter with chocolate, stirring until smooth.
Blend in ¼ cup of sugar, yolks, coffee mixture and vanilla; stir in flour (can be prepared several hours ahead and set aside at cool room temperature. Reheat before continuing.) Beat whites in large bowl until soft peaks form; gradually add remaining ½ cup sugar, beating, until whites are stiff but not dry.
Fold ¼ of whites into chocolate mixture, then fold chocolate back into whites (be careful not to deflate – a few streaks of white may remain).
Gently turn batter into prepared dish.
Sprinkle lightly with sugar.
Bake 5 minutes.
Reduce oven temperature to 400F and continue baking until puffed, about 20 minutes (center will remain moist).
Serve immediately with sauce.
(and remember – A SOUFFLE WAITS FOR NO ONE).
Vanilla Ice Cream Sauce: Let ice cream soften 10 minutes; add rum and beat until smooth.