Set crust in a 9" pie pan and refrigerate the pie while you prepare the filling.
In a large bowl, whisk together the sugar, flour and cornstarch. Add the berries, lemon juice and melted butter. Stir until the berries are coated. Scoop the mixture into the prepared crust.
Roll out the top crust, making a lattice if you like; place it over the berries. Trim any excess overhang, and crimp the edges together. Cut several slashes to allow steam to escape (if you haven't made a lattice crust). Spritz with water, and sprinkle with sparkling sugar or cinnamon-sugar.
Bake the pie for 15 minutes at 425° F, then reduce the oven heat to 350° F and bake for another 40 to 50 minutes, covering the edges if they seem to be browning too quickly. When done, the filling will be bubbling, and the crust golden brown.
Remove the pie from the oven, and cool it for at least 1 hour before serving.