Wash and peel peaches; slice to the size you prefer and set aside. Combine the sugar, cornstarch and water. Bring to a rolling boil for 3 - 5 minutes and then remove from heat (be sure the mixture thickens or the pie will be runny). Cool for 15 minutes; add the Peach jello and mix well.
Place the sliced peaches in the Shortbread crust. Pour the gelatin mixture on top and refrigerate until congealed. Once the pie has been refrigerated for several hours, top with Cool Whip and keep refrigerated.
Note: I heard that Wal-Mart's brand of Peach jello is the best.
Optional: I combined 2 ounces of cream cheese and one heaping tablespoon of powdered sugar; mixed well and spread on the crust before placing the peaches on it. This is actually very good on the Strawberry pie but it was good on this pie as well. This is just a matter of preference and certainly not necessary at all.