Butter 15 x 11 x 12 inch glass casserole dish. Make pastry by cutting shortening into sifted flour and salt until mixture resembles coarse meal.
Sprinkle 2 or 3 T. cold water, more if needed, into flour mixture to make stiff, pliable dough. Divide dough into 3 parts with the bottom crust slightly larger than the other two portions. Roll the 3 portions out on a lightly floured surface. Pat the large bottom crust into bottom of pan and adjust to fit so that it rests with edges halfway up sides of pan. (I have also made this pie with store bought crusts I lifted from their aluminum pan and patted to fit in the glass casserole.) In a large bowl, mix 2 cans of cherries and their liquid with sugar, 1/4 tsp. salt, cinnamon, vanilla, and the flour dissolved in water. Pour half of the cherry mixture into the pastry-lined pan. Add middle crust. If crust is a bit to large and has a few wrinkles in it, that is ok. Tuck to seal with bottom crust. Leave about half the height of the pan available for reserved filling and the final crust. Prick with fork to create steam vents. Cube half of the butter and dot the crust. Sprinkle with additional sugar. Bake in preheated oven at 400 for about 25 minutes. Remove from oven.
Pour remaining cherry mixture over the top crust. Cover with third rolled-out pastry. seal by pressing edges of pie pastry against sides of pan. Prick with fork to release steam. Cube remaining butter and dot crust. Sprinkle with sugar.
Return to oven and bake 10 minutes at 400, reduce heat to 350 and bake until top crust is golden brown. Remove and serve hot or cold. Serve with whipped cream or ice cream!