First, in a small saucepan on med/high heat, add white granulated sugar and blueberries. Heat until it starts to bubble and cook about 5-10 minutes. Remove from heat. Stir in corn starch to thicken the blueberry sauce. Let cool.
Next, in a large mixing bowl add heavy cream and powdered sugar. Using a mixer, mix on high until it becomes the consistency of whipped cream. It will take a few minutes.
Then, add the condensed milk to the whipped cream along with the blueberries. Stir together by hand until well combined.
Next, pour the mixture into a graham or shortbread pie crust, cover and put in your freezer for 4 hours. Serve frozen but, this pie can be stored and eaten from the refrigerator.
Store this pie in the freezer for up to 6 months or refrigerate for up to 5 days.