PREHEAT oven to 300° F. Spray bottom of 9-inch fluted tart pan with removable bottom with nonstick cooking spray.
COMBINE flour, cornstarch, pumpkin pie spice and salt in small bowl.
BEAT butter and powdered sugar in large mixer bowl until creamy. Beat in pumpkin until combined. Add flour mixture and mix until just incorporated. Spread dough into prepared pan; smooth top.
BAKE for 80 minutes or until firm and golden brown. Immediately sprinkle top with sparkling sugar. Cool for about 10 minutes; remove side from pan. Use long, serrated knife to cut into wedges. Serve warm with ice cream.