Preheat the oven to 400 degrees F.
Pie Crust: Mix flour and shortening. Add salt and cold water. Add all the cold water at once and mix delicately. Form a ball and refrigerate for 2 hours.
Once dough is chilled, flour your worktop. Divide dough in half. Roll out 2 pie crusts. One should be slightly larger than the other, this will be your bottom crust.
Meat Filling: Heat the oil in a large pot. Add the pork and onion and cook over medium-low heat for 45 minutes, stirring often. When pork is cooked remove fat from pan. Add grated potato, salt, pepper, and allspice, to taste. Stir well, and let mixture rest for 20 minutes.
Preheat the oven to 400 degrees F. Butter the bottom of 9-inch pie plate. Place the bottom crust in the pie plate and poke several holes in the crust with a fork. Make sure an ample amount of crust spills over the edges of the pie plate. Fill the crust with the meat mixture. Level with a spatula. Wet edges of bottom crust and place top crust over meat mixture. Press top crust onto meat mixture to eliminate any air holes. Beat together the egg and the milk to make an egg wash. Pinch the crust edges together and brush the top crust with the egg wash.
Bake for 10 minutes. Reduce heat to 350 degrees F and continue baking for 15 minutes or until crust is golden brown.
Slice and serve hot or cold.