Step 1

Preheat oven to 425º Line a 9-inch pie plate with 1 layer of pastry; set aside.

Step 2

Combine 1 cup of water and the salt in a large saucepan. Add sweetpotatoes; cover and bring to a boil over high heat. Reduce heat and simmer until sweetpotatoes are just barely tender when pierced, about 5 minutes. Drain slices, rinse with cold water until cool to touch. Drain slices well; transfer them to a large mixing bowl.

Step 3

To sweetpotatoes, add sugars, lemon juice, flour and pumpkin pie spice. Toss gently with a spatula until slices are evenly coated. Spoon sweetpotatoes into pastry-lined pie plate; dot top of potatoes with butter. Place top pastry over filling and crimp top and bottom pastries together to make decorative edge. Cut 3 to 4 slits in the top to allow steam to escape.

Step 4

Bake in oven until crust is browned and sweetpotatoes are tender when pierced, about 50 minutes.

Step 5

Cool pie on wire rack at least 1 hour. Serve warm or cool.

Step 6

If edges of crust start to brown too quickly, drape lightly with strips of foil.