Position oven rack to lowest setting, and remove the middle rack. Preheat oven to 425°.
Coat a 1 1/2-quart soufflé dish with cooking spray. Sprinkle evenly with 2 tablespoons granulated sugar. Set aside.
Pierce potatoes with a fork; arrange on paper towels in microwave oven. Microwave at high 10 minutes or until tender, rearranging potatoes after 5 minutes. Let stand 5 minutes. Peel potatoes. Combine potatoes and butter, and mash with a potato masher until smooth.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, potato mixture, half-and-half, and next 6 ingredients (through egg yolks) in a food processor; process until smooth. Transfer potato mixture to a large bowl.
Place egg whites in a large mixing bowl; beat at high speed with a mixer until soft peaks form. Add remaining 2 tablespoons granulated sugar, 1 tablespoon at a time, beating until stiff peaks form (do not overbeat). Gently fold one-fourth of egg white mixture into potato mixture; gently fold in remaining egg white mixture. Gently spoon mixture into prepared dish. Sharply tap dish 2 or 3 times on the counter to level. Place dish on a baking sheet; place baking sheet in a 425° oven. Immediately reduce oven temperature to 375° (do not remove soufflé from oven). Bake 1 hour or until soufflé is puffy, golden, and set. Serve immediately.