Preheat oven to 400°.
Coat 6 (6-ounce) ramekins or custard cups with cooking spray. Divide 2 1/2 tablespoons sugar evenly among the 6 ramekins, and turn to coat insides of ramekins with sugar.
Combine 6 tablespoons milk and raspberries in a blender or food processor; process until smooth. Strain raspberry mixture through a sieve over a large bowl, pressing with back of a spoon to remove as much liquid as possible. Discard solids in sieve. Add egg yolks to raspberry mixture; stir with a whisk until smooth. Combine remaining 2 tablespoons milk and cornstarch, stirring with a whisk. Add cornstarch mixture to raspberry mixture; stir well.
Place egg whites in a large bowl; beat with a mixer at high speed until soft peaks form. Gradually add 1/3 cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Gently stir one-fourth of egg white mixture into raspberry mixture; gently fold in remaining egg white mixture. Fold in chocolate just until combined. Spoon into the 6 prepared ramekins, and place ramekins on a baking sheet.
Bake at 400° for 14 minutes or until soufflés are puffed and lightly browned. Serve immediately.