Adjust oven rack to the lower third position. Preheat oven to 425°F (218°C).
Roll out one of the pie crusts, transfer to a 9-inch pie plate, gently fit it in the dish, and trim any excess dough from the edges, then place in the refrigerator. Roll out the second pie crust and either cut out lattice strips, decorations, or leave whole.
Add the halved cherries, sugar, cornstarch, lemon juice, and vanilla extract to a large mixing bowl and mix until all of the cherries are well coated.
Remove the pie plate with the pie crust from the refrigerator and scoop the cherry pie filling into the pie crust. Place the pieces of butter on top of the filling.
Next, use the second pie crust to decorate the top (if leaving it whole, make sure to cut some slits in the top), and decorate the edges.
In a small bowl, whisk together the egg and milk until fully combined. Brush the top and edges of the pie crust with the egg wash. Sprinkle with coarse sugar if desired.
Place in the oven and bake at 425°F (218°C) for 20 minutes, then reduce the oven temperature to 375°F (180°C) and continue baking for an additional 30-35 minutes or until the crust is golden brown and the filling is bubbling. If the edges of the pie crust begin to brown too much, use a pie crust shield or foil to cover them.
Remove from the oven and place on a wire rack to cool completely, then slice into pieces, and enjoy!