Preheat oven to 350 degrees F.
Allow store bought pie crust to sit on the counter while you prepare the filling. If using homemade dough, roll into a circle and place onto greased jelly roll pan or one that is lined with a silicone baking mat. For store bought crust, unroll and place onto jelly roll pan as you would the homemade crust.
In a large mixing bowl, combine the strawberries and blueberries with the cornstarch and sugar. Stir to coat.
Place in the center of the pie crust leaving room around the edges to fold.
Bring the edges up over part of the fruit filling, overlapping them as needed until all the edges have been brought up around the fruit. Gently press together the areas where the crust overlaps to help ensure that they stay up around the fruit.
In a small bowl, beat the egg with a fork. Using a pastry brush, brush the edges with egg.
Sprinkle some sugar over the egg and filling.
Bake 30 minutes or until golden brown.
Serve. You can top it with whipped cream or vanilla ice cream before serving if desired.