Prepare the filling: In a large bowl, combine frozen cherries, sugar, cornstarch, and lemon juice. Let sit for 10 minutes to macerate.
Prepare crust: Roll out one pie crust into a 9-inch pie dish. Pour in the cherry mixture and dot with butter. Cover with second crust, seal edges, and cut slits on top.
Brush the top crust with egg wash and a bit of milk. Bake in a preheated oven at 375°F (190°C) for 60 minutes until golden and bubbly. Use baking sheet underneath.
Cool on a cooling rack for at least 4 hours before serving.
Slice and serve on its own or with whipped cream or ice cream.
Notes
For best results, allow the pie to cool completely before slicing to let the filling set properly.