Prepare pie crust by stirring together the flour and salt. Using a pastry cutter or a food processor, cut the shortening and butter into the flour until the mixture resembles coarse crumbs.
Sprinkle 2 tablespoons of the ice water over the flour mixture and gently stir it in using a fork, then repeat with the remaining water, adding 2 tablespoons at a time, just until the dough starts to come together. Use your hands to press the dough into a ball, then flatten into a disc and wrap tightly in plastic wrap and refrigerate for at least 1 hour.
Season the meat with the salt and pepper. In a large skillet or dutch oven over medium-high heat, add the oil. When the oil is hot, add the seasoned meat, working in batches if necessary, and searing until nicely browned on all sides, about 8 to 10 minutes. Remove from skillet and set aside.
Reduce the heat to medium and add another tablespoon of oil if the skillet is looking dry, then add the onions and garlic and sauté for 2 minutes.
Add the carrots, celery and potato and cook for another 6 to 8 minutes, until the vegetables are starting to soften a bit and the onions look translucent. Add the mushrooms and continue to cook 2-3 minutes more.
Add the chopped rosemary, thyme, and oregano and cook for another 30 seconds, then sprinkle the flour over the vegetables and stir to coat everything evenly. Cook for another 2-3 minutes.
Stir in the beef broth until flour is completely dissolved, then add the seared beef back to the vegetables and gravy. Cover the skillet or dutch oven with a lid and reduce the heat to low. Simmer gently for 1 ½-2 hours or until the meat is tender, stirring occasionally. Allow the chilled pie crust dough to sit on the counter for 10 minutes before rolling it out to assemble the pie.
Pour the beef stew filling into a deep pie dish until ¾ full. Any remaining stew can be used to make individual size pies or eaten plain.
Roll out the pie crust on a floured surface, then transfer it to cover the beef filling, making sure there is some overhand so the crust doesn't shrink entirely away from the side of the pie dish while baking.
Decorate the pie with leaves cut from scraps of pie crust, if desired and brush the entire crust with the beaten egg. Cut slits in the top of the pie to allow steam to escape, then bake for 25 to 30 minutes in a 400 degree oven until the filling is bubbling and the crust is golden brown.
Remove from the oven and allow to cool for 30 minutes before serving.