In a large bowl, whisk together the all-purpose flour and ½ teaspoon salt.
Add the cold unsalted butter and cold shortening; cut into the flour with a pastry blender or fingertips until the mixture resembles coarse crumbs with pea-sized pieces.
Gradually add the ice water, one tablespoon at a time, mixing until the dough just comes together; form into two flat discs, wrap in plastic wrap, and refrigerate for at least 30 minutes.
In a separate large bowl, combine the cubed beef skirt steak, Russet potatoes, yellow onion, and rutabaga; season with 1 teaspoon salt and ½ teaspoon black pepper and toss to coat.
Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
On a lightly floured surface, roll one dough disc into a 12-inch circle about ⅛-inch thick and cut two 7-inch circles; repeat with the second disc to yield four circles.
Spoon about 1½ cups of the filling onto one half of each pastry circle, leaving a ½-inch border, then drizzle 1 tablespoon beef broth over each.
Moisten the pastry edges with water, fold the empty half over the filling to form a half-moon, press to seal, and crimp the edges in the traditional Cornish style.
Cut a small slit or two on top of each pasty to allow steam to escape.
In a small bowl, whisk the large egg and 1 tablespoon water; brush the egg wash over the tops of the pasties.
Bake at 400°F (200°C) for 20 minutes, then reduce the oven temperature to 350°F (175°C) and continue baking for 25–35 minutes, until golden brown and the filling is tender.
Let the pasties cool on the baking sheet for about 10 minutes before serving.