Roll the pie crust out into a 12-inch circle and place it into a 9-inch pie pan or tart pan. Crimp edges or cut off excess pie crust to fit pie tart pan. Place the pie crust into the refrigerator for at least 1 hour before assembling the pie.
While the pie crust is chilling prepare the cherries by washing, drying, and pitting. Slice in half or leave whole.
Mix together sugar, flour, sour cream, and salt and set aside to use for the filling.
For the crumble topping, mix together the flour, sugar, and butter until crumbly, using your fingers or 2 forks.
Remove the pie crust from the refrigerator. Whisk the egg with 1 tablespoon of water and brush the bottom of the pie crust with the egg wash. Spread the cherries evenly over the pie crust. Pour the sour cream mixture evenly over the cherries and tap the pie pan gently on the counter to distribute custard. Top with the crumble topping.
Place the cherry pie onto a sheet pan and bake the cherry pie until the center of the pie no longer jiggles. The pan will protect the oven if any cherry juice happens to bubble over while the pie bakes. If using Fresh Cherries: Bake cherry pie for 40-45 minutes in a 350 degree If using Frozen Cherries: Bake pie for 55 to 65 minutes at 375 degrees, or until the center of pie is set.
Allow pie to cool to room temperature. Then cover with plastic wrap and refrigerate. The pie is best served after being refrigerated for 12-24 hours.
This Cherry Custard Pie is best served after refrigerated for 12-24 hours, which gives the flavors time to meld together and the custard to chill and set up. Cherry Pie will last in the fridge for 3-5 days but it is best enjoyed within 3 days. Be sure to store it in the refrigerator once it cools after baking.To freeze the cherry pie, allow the pie to cool fully. Wrap the pie in plastic wrap and then place it into a larger freezer-safe storage bag. Freeze for up to 3 months. To enjoy, let the pie thaw in the refrigerator for 24 hours.I have substituted plain Greek yogurt for the sour cream in the custard for this pie, with just as delicious results.Cherries: Slicing the cherries will allow the custard to more evenly coat the cherries and every bite, and will make the cherry pie easier to cut. I love the presentation of using whole cherries though.Egg-Wash: If you are egg-free, skip the egg-wash step or brush your crust with milk or a thin layer of cherry jam. Be sure to use SWEET cherries, not sour cherries for this pie recipe.