Prepare pastry according to directions, then roll out the larger of the two doughs and place in bottom of pie plate. Chill while preparing filling.
For filling, combine the cornstarch, sugar, lemon zest. Place berries in separate bowls (or all together), then divide sugar mixture up between bowls and gently toss to combine.
If desired, use a pastry brush to brush the bottom crust with some of the egg whites (keep crust from getting soggy). Spoon in filling, sprinkle with cinnamon and dot with butter if desired.
Roll out top crust, or cut into shapes and place on top of berries. For a golden crust, brush with the egg whites, and sprinkle on some coarse sugar.
Place pie on a baking sheet (to prevent any spillage) and bake at 425°F for 15 minutes. Reduce heat to 350°F and continue baking for another 35-40 minutes or until crust is golden.
Set on a wire rack and allow to cool to room temperature.
Notes
Instead of brushing egg whites on the top crust to help browning, you can brush on milk, or omit completely.