In a medium to large pot, mix 3 cups fresh blue berries, 1 cup sugar, 1/3 cup flour, ¼ cup water, 1 ½ tablespoons lemon juice, and 1 teaspoon vanilla extract. Stir together and place over low to medium heat. Bring the mixture to a boil, and then reduce the heat to low. Cook 10 minutes, stirring occasionally. Spoon half of blueberry mixture into an 11-inch by 7-inch baking dish that has been sprayed with cooking oil spray. Roll 1 pie crust 10 1/8-inch thickness on a lightly floured surface, and cut dough into an 11-inch by 7-inch rectangle. Place the rectangle of dough of top of the blueberry mixture. Bake at 450 degrees for about 10 minutes, until lightly brown. Let the remaining half of the blueberry mixture cool to room temperature for ease in making a lattice top crust. Then spoon remaining blueberry mixture over the top of the baked crust. Roll remaining pie crust to 1/8-inch thickness, and cut into 1-inch strips. Arrange in lattice design over blueberry mixture. (There is a Quick Tip on making a lattice pie crust in bettyskitchen to help you, if you need it. If you prefer not to have a lattice top, just form another 7-inch by 11-inch rectangle of pie crust, place it on top, cut a few slits in it to let steam out, and place it over the second layer of blueberry mixture.) Bake about 10 minutes at 450 degrees, or until crust is brown and filling is bubbly. Remove from oven and cool for about 10 minutes. Serve in a bowl with a couple of scoops of vanilla ice cream! I hope you enjoy this summery treat! --Betty