In a medium bowl, combine cooked sweet potatoes, skim milk, maple syrup, allspice, cinnamon, salt, eggs, vanilla and butter. Mix with a hand mixer until ingredients are evenly combined.
Divide and pour batter into the two pie pans and bake for 15 minutes. Reduce oven temp to 350°F, then bake another 45 mins or until center of each pie is set. Let cool then serve with 1 tablespoon whipped topping.