Step 1Sift together the flour and salt. Remove 1/3 cup of the mixture and mix with 1/4 cup water into a paste.
Step 2Cut the shortening and butter into the flour mixture. Incorporate the paste quickly into the flour and form into 2 balls; the second ball should be about 3/4 the size of the bigger ball. Flatten into disks, wrap in plastic wrap and refrigerate 1 hour.
Step 1Mix together the sugar, cornstarch and salt; set aside.
Step 2Bring the cherry juice to a boil in a saucepan. Add the sugar mixture and cook until thickened, about 2 minutes. Remove from the heat and stir in the cherries, butter, lemon juice, lemon zest and rum. Let cool to warm, 10 minutes, before filling crust.
Step 1Heat the oven to 425 degrees.
Step 2Roll out the larger dough disk on a lightly floured surface into a circle large enough to fit into a 9-inch pie plate with a 1-inch edge. Place the circle in the pie plate, then fill with the Cherry Filling. Roll out the remaining dough into a 12-inch rectangle. Cut the dough into lengthwise 1-inch strips. Arrange the strips on top of the pie in a lattice pattern. Roll and crimp the edges of the crust.
Step 3Set the pie in the center of the oven, placing a sheet of foil beneath it to catch any drips. Bake until the crust is golden and the filling is bubbling in the center, 35 to 40 minutes. If the edges of the crust become too dark while baking, cover them with strips of foil.