Position a rack on the lowest shelf of the oven and preheat to 450 degrees . Fit the piecrust into the bottom and up the sides of a 9-inch pie dish. Crimp the edges to form a 1/4-inch-high border. Prick the bottom and sides of the crust with a fork. Bake until pale golden-brown, 8 to 10 minutes. Lower the oven temperature to 325 degrees .
Meanwhile, in a large bowl, whisk together the pumpkin puree, granulated sugar, brown sugar and eggs until smooth. Whisk in the milk, molasses, pumpkin pie spice, vanilla and salt. Pour the mixture into the piecrust and bake until the center is just set, about 55 minutes. Transfer to a rack and let cool completely.