Tourtière du Shack

Name: Tourtière du Shack
Ingredients: 3 1/3 cups all-purpose flour; 2 cups (4 sticks) chilled unsalted butter, cut into 1/2' cubes; 1 teaspoon kosher salt; 1 1/2 cups low-salt chicken broth; 1 1/2 medium onions, chopped, divided; 4 garlic cloves, chopped, divided; 5 whole black peppercorns plus freshly ground black pepper; 5 sprigs thyme; 2 bay leaves; 1 1/2 pounds boneless pork shoulder (Boston butt), cut into 2' pieces; Kosher salt; 1 tablespoon unsalted butter; 8 medium button mushrooms, stemmed and finely chopped; 1 /2 cup dry white wine; 1 1/4 pounds ground pork; 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