Bittersweet Chocolate and Pear Pie

For filling: In a large bowl, toss pears and lemon juice together. In a small bowl, combine 1/2 cup granulated sugar, the tapioca flour, cinnamon and salt. Add sugar mixture to pears; toss with hands to coat evenly.

Unwrap one disc of pastry and place it on a lightly floured surface. Bang the dough with your rolling pin about 4 times, from left to right. Flip and bang left to right again. Begin rolling the pastry from the center forward, using less pressure on the edge. Every few rolls, rotate the disc a quarter-turn. If pastry starts to stick, lift it gently and sprinkle more flour underneath. If the top gets sticky, flip the disc over. Continue rolling and rotating until the circle is 12 to 13 inches across. Loosely fold the circle in half and transfer to a 9-inch pie plate. Unfold dough and gently but snugly press it into the corners. If any dough hangs over by more than 2 inches, trim it with kitchen scissors. (Use those scraps to patch holes or bolster spots where you don't have much overhang.)

Roll out the second disc of pastry into a 10-inch circle (or follow the directions for a lattice-top pie, below**). Slide the circle onto a parchment-lined baking sheet. Refrigerate the pastry shell and pastry top for 30 minutes.

To assemble: Sprinkle 1 teaspoon each turbinado and granulated sugar evenly all over the bottom of pie shell, followed by the chocolate and finally the pear filling. Dot pears with butter cubes. Top with the circle of pastry. Roll the bottom pastry up and inward, enclosing the edge of the top pastry circle, to form a thick rim and crimp to seal. Transfer assembled pie to the freezer for 15 minutes.

Meanwhile, preheat oven to 450°. Place a foil-lined baking sheet on the bottom rack of the oven to catch drips. In a small bowl, beat together the egg and water. Brush pie all over with egg mixture. Use a paring knife to cut steam vents in the top crust. (We pricked the pie all over with dozens of tiny slits.) Bake pie on the middle oven rack until crust is evenly golden brown, about 20 minutes. Reduce oven temperature to 325° and continue baking until pie juices are bubbling in the center, 60 to 70 minutes. Transfer pie to a wire rack to cool for 4 to 6 hours before serving.