Homemade Blackberry Pie

Bahan-bahan (8 porsi)

• 5 to 6 cups blackberries (fresh or frozen)
• ½ cup granulated sugar (*see note)
• 3 to 4 tablespoons cornstarch (*see note)
• ¼ teaspoon cinnamon
• 2 tablespoons butter
• 1 double pie crust (homemade or store bought)
• 1 egg yolk