Prepare crust--in medium bowl, stir together flour, sugar, and salt; using a pastry blender, cut in cold butter until pieces are pea size.
Sprinkle 1 tablespoon cold water over par of the flour mixture; toss gently with a fork; push moistened dough to side of bowl; repeat with additional cold water, 1 tablespoon at a time until all of the flour mixture is moistened; shape into a ball.
Preheat oven to 400°.
Roll out dough on a lightly floured surface into a 12-inch circle; transfer dough to a 9-inch pie plate; fit pastry to plate without stretching it.
Trim pastry to 1/2 inch beyond edge of pie plate; fold under extra pastry; crimp edges as desired.
Prick bottom and sides of pastry with a fork; line pastry with a double thickness of foil; bake for 8 minutes.
Remove foil; bake for 5-6 minutes more or until pastry is golden; cool on wire rack.
Decrease oven temperature to 350°.
In a big bowl, combine eggs, egg whites, sugar, and lemon juice; beat with an electric mixer on medium to high speed until thick and lemon colored.
Stir in melted butter and lemon peel.
Place blackberries in bottom of baked pastry shell.
Pour lemon mixture over blackberries.
Bake about 30 minutes or until lemon mixture is set; (cover pie crust edges with foil if concerned about overbrowning); cool on wire rack.