Preheat oven to 375°. Generously butter six 8-oz. soufflé dishes. Sprinkle butter with sugar to coat. Put dishes on a baking sheet and set aside.
Bring 1 in. water to a boil in a medium frying pan. Put chocolate, milk, and 1 tbsp. butter in a small metal bowl. Put bowl in water and take pan off heat. Stir occasionally until chocolate melts. Remove bowl from water, mix in egg yolks, and set aside.
In a large clean bowl, beat egg whites, salt, and cream of tartar until soft peaks form. Sprinkle in 6 tbsp. sugar and beat until stiff peaks form.
Whisk 1/4 of beaten egg whites into the chocolate mixture. Fold chocolate mixture into the remaining egg whites. Divide mixture evenly among prepared soufflé dishes and bake until set but still soft in the center, 15 to 20 minutes. Serve immediately, with vanilla bean cream if you like.
Note: Nutritional analysis is per serving.