Preheat your oven to 400°F (200°C). Let the refrigerated pie crusts sit at room temperature for about 15 minutes to soften slightly so they are easier to unroll.

In a large skillet or pot over medium heat, combine the ground pork, ground beef, chopped onion, and minced garlic. Cook until the meat is browned and cooked through, about 8 to 10 minutes, breaking it apart with a wooden spoon as it cooks.

Drain any excess fat from the skillet to prevent a soggy pie crust. Stir in the grated potato, beef broth, salt, black pepper, cinnamon, cloves, and allspice until thoroughly combined.

Reduce the heat to low, cover the skillet, and let the mixture simmer gently for 15 to 20 minutes. The potato should become tender and the liquid should be mostly absorbed, creating a thick, cohesive filling.

Remove the skillet from the heat and let the meat filling cool for at least 10 minutes. Meanwhile, unroll one pie crust and press it gently into the bottom and up the sides of a 9-inch pie dish.

Spoon the slightly cooled meat filling evenly into the bottom pie crust. Unroll the second pie crust and drape it carefully over the filling.

Trim any excess overhanging dough with a knife, then crimp the edges together tightly with your fingers or a fork to seal the pie. Brush the top crust evenly with the beaten egg, and cut 3 to 4 small slits in the center of the pie to allow steam to escape.

Bake for 30 to 35 minutes, or until the crust is a deep, shiny golden brown and the filling is bubbly. Let the tourtiere rest for 15 minutes before slicing, and serve warm with a side of cranberry sauce or a fresh green salad.