How to Make It
In a food processor, pulse the flour with the sugar and salt. Add the butter and shortening and pulse just until the mixture resembles coarse meal. Add the ice water and process until a dough just starts to form. Transfer the dough to a floured work surface and knead gently. Pat the dough into a disk, wrap in plastic and refrigerate for at least 1 hour.
Preheat the oven to 375°. On a lightly floured work surface, roll out the dough to an 11-inch round about 1/8 inch thick. Transfer the dough to a 9-inch pie dish and trim the overhang to 3/4 inch; fold the overhang under itself and crimp decoratively. Prick the bottom of the pie shell all over and refrigerate until firm.
Line the shell with foil and fill with pie weights or dried beans. Bake for about 20 minutes, or until lightly golden around the edge. Remove the foil and the weights and bake for about 12 minutes longer, or until the pie shell is golden brown and cooked on the bottom. Cover the rim of the pie shell with foil when it starts to brown. Leave the oven on.
Pierce the sweet potatoes and bake them for 1 hour, or until tender; cool slightly. Slit the skins and scoop the potatoes into a bowl. Mash until smooth. Whisk in the cream, brown sugar, eggs, butter, vanilla, salt, cinnamon, allspice and nutmeg and scrape into the pie shell.
Bake the sweet potato pie for 15 minutes. Turn the oven down to 350° and continue to bake for about 40 minutes longer, or until the filling is set. Transfer the pie to a wire rack to cool. Serve warm or at room temperature with vanilla ice cream and Praline Sauce.