Mix the filling ingredients with the sour cherries.
Roll out the bottom crust and place it in the pie plate.
Roll out the second half of the dough and cut into strips for the lattice.
Assemble the lattice top crust over the cherry filling.
Fold the edges of the lattice and crimp the border.
Brush the crust with beaten egg and sprinkle with Demerara sugar.
Bake at 425°F for 20 minutes, then reduce temperature to 350°F and bake for 2 to 2.5 hours.
Let the pie cool for at least 24 hours before serving.
