PREHEAT oven to 375º F. Adjust oven rack to the lower-middle position of the oven. Grease six 6-ounce soufflé dishes or ramekins with 1 tablespoon butter. Coat bottom and sides with 2 tablespoons sugar; dump out any excess.
MICROWAVE chocolate and 1/4 cup butter in large, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 minute; STIR. Pieces may retain some of the their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until smooth; cool to room temperature.
WHISK egg yolks, one at a time, into chocolate mixture. Whisk in vanilla extract and salt.
BEAT egg whites in large mixer bowl until soft peaks form. Beat in cream of tartar. Gradually beat in 1/4 cup granulated sugar until stiff peaks form. Fold 1/2 cup egg white mixture into chocolate mixture to lighten. Fold in remaining egg white mixture gently but thoroughtly. Divide batter among prepared ramekins. Smooth tops and clean excess batter from rims. Place on baking sheet.
BAKE for 15 to 17 minutes or until puffed and center still moves slightly. Serve immediately.