Scrub and pierce sweet potatoes. Bake at 350° for 1 to 1-1/4 hours or until very tender.
Cut sweet potatoes in half; scoop out pulp and place in a large bowl. Mash with milk and egg substitute. Stir in the brown sugar, flour, raisins, orange zest, pumpkin pie spice, vanilla and salt until blended.
Transfer to a 1-1/2-qt. baking dish coated with cooking spray. Cover and bake at 350° for 1-1/4 to 1-1/2 hours or just until top is set. Cool on a wire rack for 1 hour. Refrigerate for at least 2 hours. Serve with whipped topping.