1/8 teaspoon cinnamon
1/8 teaspoon ground cloves
3/4 cup grated, peeled russet potato
All-purpose flour (for surface)
1 large egg yolk, beaten to blend
A 9"-diameter deep dish glass or ceramic pie dish
Step 1. Prepare the Crust
Pulse flour, butter, and salt in a food processor until pea-size pieces of butter form. Transfer to a medium bowl. Add 1/4 cup ice water and stir just until shaggy clumps form, adding more water by teaspoonfuls if dry. Divide dough in half; flatten each half into a disk. Wrap disks in plastic wrap and chill for at least 2 hours. DO AHEAD: Dough can be made 2 days ahead. Keep chilled.
Transfer pork shoulder to a work surface. Shred meat with your fingers and transfer to a medium bowl. Strain pan juices through a fine-mesh sieve; add 1/2 cup juices to pork; discard solids in strainer.
Add ground pork, cinnamon, and cloves. Cook, stirring to break up into small pieces, until pork is cooked through, about 5 minutes. Add potato. Cook until potato is soft, about 10 minutes. Remove from heat. Stir in shredded pork with juices. Season to taste with salt and pepper; let cool slightly. Chill until cold, about 1 hour. DO AHEAD: Can be made 1 day ahead. Cover and keep chilled.
Roll out 1 dough disk on a lightly floured surface into a 12" round. Transfer to pie dish, leaving overhang. Fill with cooled meat mixture. Roll out remaining dough disk into a 10" round. Place dough over meat filling. Fold overhang over top crust and crimp edges. Brush crust with egg yolk. Cut three 2" slits in top crust. Chill for 1 hour.
Preheat oven to 400°F. Bake tourtière for 30 minutes. Reduce heat to 350°F; bake until crust is golden brown and filling is bubbling, 40-50 minutes. Let cool for 20 minutes before serving.