3. In a large skillet with a lid, or a Dutch oven, heat the ground beef and pork over medium heat. Cook, stirring to break up the meat, until it’s browned and cooked through. With a slotted spoon, remove the meat to a plate or bowl, and drain from the pan all but 2 tablespoons of fat. (Any meaty juices that are in the pan should be reserved to add later.)
4. Add the diced onion to the pot and cook until translucent, about 5 minutes. Stir in the potatoes, salt, spices, and bay leaf, coating the potatoes and onions with the spices. Stir the cooked beef and pork back into the pot along with the stock, and any reserved juices from the previous step.
5. Bring to a low boil, then reduce the heat to a simmer, cover and cook gently for 30 minutes, stirring once or twice while cooking. Transfer the mixture to a small bowl, remove the bay leaf, and cool to room temperature or chill in the refrigerator.
6. To assemble the tourtière, remove the dough from the refrigerator and on a lightly floured surface, roll one disk of the dough into a 13-inch (33cm) circle. Gently drape it into a deep 9- to 10-inch (23cm) pie plate or pan. (The authors say this can also be baked in a similar-sized skillet, with an ovenproof handle.) Scrape the meat mixture into the dough-lined pan, then roll out the second disk of dough to the same size, and drape it over the pie. Tuck the two pieces of dough that are overhanging the sides under the rim, inside the pie plate. Crimp the edges and chill the pie for one hour, or freeze it for 15 minutes.
7. To bake the tourtière, preheat the oven to 375ºF (190ºC). Brush the egg yolk over the top of the pie dough, cut a hole in the center, and make any decorative marks you wish in the top with the tip of a sharp paring knife. Bake the pie until the top is golden brown, about 45 to 50 minutes. If necessary, you can run the pie under the broiler a minute or so to get it to brown nicely. Let cool 10 minutes before serving.