4 cups frozen sour cherries, defrosted until easily separated and drained
1 cup sugar
1 tablespoon all-purpose flour, plus more for rolling out dough
2 1/2 tablespoons cornstarch
Juice and zest of 1/2 lemon
1 large egg, lightly beaten
2 tablespoons heavy cream
Preheat oven to 450 degrees. In a medium bowl, combine cherries, sugar, flour, cornstarch, lemon juice, and zest.
On a lightly floured surface, roll one disk of dough into a 12-inch round, about 1/8-inch thick. Fit into a 9-inch glass pie plate. Pour in cherry filling. Roll second disk of dough into a 12-inch round. Cut the dough into 3/4- to 1-inch strips and lay over filling, creating a lattice. Trim edges to 1-inch, and seal by crimping edges with thumb and forefinger. Place on a parchment-lined baking sheet.
In a small bowl, whisk together egg and cream. Brush over top of pie. Bake for 10 minutes. Reduce temperature to 400 degrees and bake until golden brown, and juices are bubbling, 40 to 50 minutes more. Remove from oven, and let cool for at least 2 hours before serving.