2 tablespoons unsalted butter, melted
2 tablespoons fresh lemon juice
2 tablespoons water
1 tablespoon quick-cooking tapioca
1 egg white, lightly beaten
1 tablespoon coarse or granulated sugar
BLEND together flour, butter, shortening, and salt in a bowl with your fingertips or a pastry blender (or pulse in a food processor) until most of mixture resembles coarse meal with rest in small (roughly pea-size) lumps.
DRIZZLE 4 tablespoons ice water evenly over and gently stir with a fork (or pulse in processor) until incorporated.
GENTLY squeeze a small handful. It should hold together without crumbling apart. If it doesn't, add more water, 1 tablespoon at a time, stirring or pulsing after each addition until incorporated, continuing to test. Do not overwork dough or it will become tough.
TURN dough out onto a work surface and divide into 2 portions. With heel of your hand, smear each portion once in a forward motion to help distribute fat. Gather each portion of dough and form it, rotating on a work surface, into a disk. Wrap disks separately in wax paper and chill until firm, at least 1 hour.
PLACE a baking sheet in lower third of oven and heat to 400 degrees.
WASH and dry blackberries.
TOSS together berries, granulated sugar to taste, cornstarch, butter, lemon juice, water and tapioca. Let stand, tossing occasionally, 20 minutes.
ROLL out 1 piece of dough into a 14-inch round and fit into a 9-inch pie plate. Trim edge, leaving a 1/2-inch overhang. Chill shell while rolling out top.
ROLL out remaining piece of dough into a roughly 16 x 11-inch rectangle. Cut crosswise into 11 strips with a fluted pastry wheel or a knife.
STIR berry mixture, then spoon evenly into shell. Arrange strips in a tight lattice pattern on top of filling and trim strips close to edge of pan. Roll up and crimp edge. Brush top and edge with egg white and sprinkle all over with sugar.
BAKE on hot baking sheet until crust is golden brown and filling is bubbling, 1 hour to 1 hour and 10 minutes.
CHECK pie after 45 minutes. If edge of crust is browning too quickly, cover edge with foil or a pie crust shield and continue baking. Cool completely on a rack before serving.
Makes 8 servings.