1. Preheat oven to 350°F (177°C). Grease an 8-by-8-inch baking pan.
2. Start the crust : In a food processor combine cold butter, flour, sugar, cinnamon, salt for about a minute. The mixture will look clumpy once it's come together.
3. Use 3/4 of the mixture and spread evenly into the baking pan. Make sure all the corners are sealed. Set aside the remainder 1/4 of the mixture for the topping.
4. For the filling: Combine the egg, sour cream, sugar, flour, cornstarch, vanilla extra, and the lemon juice. Once this mixture is combine gently fold in our blueberries. You can add more than 1 1/2 cups if you would prefer. Pour over the evenly pressed crust.
5. Use the remainder 1/4 of the crust, and crumble over the blueberry filling.
Bake: 45-50 minutes or until the edges and top are golden brown. Cool for 15 minutes before cutting into the pie. Leftovers can be stored covered in room temperature or fridge.