Cut shortening into flour until the shortening is the size of peas. Add salt and stir.
Put egg in a one-cup measure, beat egg with fork, then add vinegar and fill remainder of cup with water.
Add egg mixture to flour mixture. Mix till water mixture is completely incorporated. Dough will be sticky. If the dough is still too dry to stick together, add water a few tablespoonfuls at a tine. If you live at a high elevation, you will need to add 1/4-1/2 cup more water. Cover with plastic wrap to keep moist until you are ready to use it.
Roll out half of the pie dough into a large rectangle. Set the sheet pan on top to measure and make sure it's the correct size. Gently roll up the dough, then unroll onto the sheet pan, being careful not to break it. Trim the edges with a knife.
Pour all of the cherry pie filling into the crust.
Take the other half of the pie dough and roll it into a large rectangle. Cut it into wide strips and place them over the pie filling. Altrernately, you may cut little slits or designs into the crust, then carefully roll it up and place on top of filling, and unroll.
Wet the edges of the bottom crust, so the top crust will stick and not open up when baked.
Brush top crust with beaten egg, and sprinkle with sugar. This makes a beautiful, golden brown crust!
Bake for one hour, or until the crust is golden brown.
Notes
You can use any flavor of pie filling in this recipe. Try blueberry, blackberry, or apple!