Cook sweet potatoes in boiling water 15 minutes or until tender; drain well and cool. Preheat oven to 350°.
Place potatoes and applesauce in a food processor; process until smooth. Add egg yolk, vanilla, salt, and cinnamon; process until smooth. Spoon into a bowl; set aside.
Beat egg whites until stiff peaks form. Gently stir one-third of egg whites into potato mixture; gently fold in remaining egg whites. Spoon into a 1 1/2-quart soufflé dish coated with cooking spray.
Combine sugar, flour, and margarine; sprinkle over potato mixture. Bake at 350° for 35 minutes or until set.
Note: Cover and refrigerate potato mixture, without topping, for up to 24 hours, if desired. Uncover, sprinkle with topping, and bake at 350° for 45 minutes.