Bake sweet potatoes at 350° for 1 hour or until tender; cool.
Fit piecrust into a 9-inch pieplate according to package directions; fold edges under, and crimp.
Peel potatoes, and beat at medium speed with an electric mixer until smooth. Add sugar and next 7 ingredients, beating until blended. Pour into piecrust.
Bake at 425° for 15 minutes. Reduce oven temperature to 350°, and bake 1 hour and 20 minutes or until a knife inserted in center comes out clean. (Shield crust with aluminum foil to prevent excessive browning, if necessary.) Garnish, if desired.