Cook sweet potato in boiling water to cover 15 minutes or until tender; drain. Transfer sweet potato to a large bowl. Beat at medium speed of an electric mixer until smooth. Add milk and next 8 ingredients; beat at low speed until blended.
Beat egg whites at high speed of an electric mixer until stiff peaks form. Fold one-third of beaten egg whites into sweet potato mixture; fold in remaining egg whites. Spoon mixture into an ungreased 2-quart souffle dish. Bake, uncovered, at 325° for 55 minutes or until golden. Serve immediately.