Place the cherries in a large bowl then add sugar, lemon juice, and cornstarch. Mix well. Set aside.
Preheat the oven to 375 degrees
Roll out two pie shells in a rectangular shape to cover most of the jelly roll pan. Use a third shell to add to the top and bottom to complete the coverage.
Press the rolled pie shells into the pan and cut off any excess dough.
Add the cherry filling mixture to the pie dough.
Use the final pie shell to cut a couple of strips for the edges and several stars in different shapes.
Add the cut pie dough and star shapes to the pan using a little water where the dough meets to help it stick together. Crimp the sides with a fork or your fingers.
Make an egg wash by whisking an egg and 1 tablespoon of water together in a small bowl. Brush all over the crust and star shapes.
Sprinkle coarse sugar all over the top.
Bake for 50 minutes until the crust is golden and the filling is bubbling.
Remove and allow the pie to cool for 30 minutes before setting it into the refrigerator for 1 hour to set up.
Bring the cherry slab pie out an hour before serving to come back to room temperature.
Notes
You can keep the slab pie covered on the counter for a day or two.Or, you can refrigerate it for a few extra days.
Nutritional information is provided as a courtesy and is an estimate only. This information comes from online calculators. Although attempts have been made to provide accurate nutritional information, these figures are only estimates.