Preheat your oven to 375°F.
To make the pie crust, combine the flour and salt in a large mixing bowl. Cut the shortening or butter into the flour mixture until it resembles coarse crumbs.
Gradually add the ice water, one tablespoon at a time, while stirring with a fork until the mixture forms a ball.
Turn the dough onto a lightly floured surface and roll it out into a 12-inch circle. Place the dough into a 9-inch pie dish and trim the edges. Prick the bottom of the crust with a fork.
Bake the pie crust for 10-12 minutes, or until lightly browned. Remove it from the oven and set it aside to cool.
To make the filling, cream together the butter, granulated sugar, and brown sugar in a large mixing bowl until light and fluffy.
Add the mashed sweet potatoes to the mixture and beat until well combined.
Beat in the eggs, one at a time, until well incorporated.
Add the evaporated milk, vanilla extract, cinnamon, nutmeg, allspice, and salt to the mixture and beat until smooth.
Pour the filling into the prepared pie crust.
Bake the pie for 45-50 minutes, or until a knife inserted into the center comes out clean.
Remove the pie from the oven and let it cool on a wire rack for at least 30 minutes.
Serve the pie warm or at room temperature with a dollop of whipped cream.