Roll out the first chilled pie crust into a 12-inch circle. Gently place the crust into a 9 or 10-inch deep pie dish, carefully pressing the dough into the bottom and up the sides. Refrigerate for 30 minutes.

Remove the second crust from the fridge and roll into a 12-inch circle. Using a pastry wheel or pizza cutter, cut the dough lengthwise into stripes. Use a star cookie cutter to cut some stars. Place the designs on a parchment paper lined baking sheet, and freeze while you prepare the filling.

In a small bowl, whisk together the potato starch and sugar. Reserve.

Add 1 teaspoon of lemon juice to the strawberries and the remaining 2 teaspoons to the blueberries. Mix to combine. Let the berries sit for at least 5 minutes to release the excess liquids.

Fold a piece of aluminum foil to form a thick and long strip. Place it into the pie dish, blocking off a 90° wedge of the crust. Spread the blueberries into that smaller section and the strawberries into the larger section. Carefully remove the foil, arranging the berries so they don't invade each other's spaces.

Remove the flag designs from the freezer and arrange on top of the berries. The stars go over the blueberries and the strips over the strawberries.

Make an egg wash by whisking one egg with 1 tablespoon of milk. Brush over the crust and designs. If desired, sprinkle the crust and designs with sugar.

Cover the edges of the pie with a crust shield or foil.

Remove the pie from the oven and let it cool for at least one hour before serving.