1. Into 2-quart saucepan, measure flour and V* cup sugar; slowly stir in milk until smooth. Cook over medium heat, stirring constantly, until mixture thickens and boils; continue to cook 1 minute, stirring. Remove saucepan from heat.
2. Stir chocolate into mixture until melted. Rapidly beat in egg yolks all at once until well mixed; refrigerate to cool to lukewarm, stirring occasionally.
3. Preheat oven to 375°F. Grease 2 1/2-quart souffle dish with butter or margarine and lightly sprinkle with sugar.
4. In large bowl, with mixer at high speed, beat egg whites and salt until soft peaks form; gradually sprinkle in 1/4 cup sugar, beating until sugar completely dissolves and whites stand in stiff peaks. With rubber spatula, gently fold chocolate mixture, one-third at a time, and vanilla into egg whites until blended.
5. Pour mixture into souffle dish. With back of spoon, about 1 inch from edge of dish, make 1-inch-deep indentation all around in souffle mixture (the center will rise higher than the edge, making a top-hat effect when the souffle is done). Bake 35 to 40 minutes, until knife inserted under top hat comes out clean.
6. Meanwhile, if using whipped cream, beat heavy or whipping cream until soft peaks form; cover and refrigerate.
7. When souffle is done, lightly sprinkle with confectioners' sugar and serve immediately, with whipped cream if you like.