Make the pie crust: Stir together the flour, sugar, and salt then cut in the butter into the flour until the mixture resembles coarse crumbs.
Add a small amount of ice water, and mix in (adding more as needed), until the dough starts to come together.
Divide the dough into two even discs and wrap tightly in plastic wrap. Refrigerate for at least 1 hour.
Make the filling: In a medium saucepan, whisk together the sugar, cornstarch, salt, butter and about 1/4 of the liquid from the cherries. Strain the rest of the liquid from the cherries then add those as well. Bring the mixture to a simmer over medium heat, until thick and bubbly, about 5 to 7 minutes. Cool completely.
Assemble the pie: Preheat oven to 215°C then roll out the bottom pie crust and use it to line a 9-inch pie plate. Spoon the cherry pie filling into the bottom crust.
Roll out the remaining crust and make a lattice crust, or leave the crust solid using a knife to poke holes for for venting. Seal the edges, either by crimping then brush the top crust with the beaten egg and sprinkle with sugar, if desired.
Bake for 10 minutes at 215°, then decrease the oven temperature to 190°C and finish baking for 45 minutes (the top crust may need to be covered in aluminum to prevent burning). Cool completely before serving.
10 servings