Blueberries and nectarines pair exceptionally well -- especially if they're baked in a summer pie.
Make piecrust: Sift flour and salt together into a large bowl. Blend in shortening with a pastry blender or your fingertips until mixture resembles coarse meal. Stir in ice water a little at a time until dough comes together.
Divide dough in half. On a lightly floured sheet of parchment paper, roll each half with a floured rolling pin into an 11-inch round. Transfer one round to a 9-inch pie plate, gently pressing it in to fit. Transfer second half to a baking sheet, and cover with parchment paper. Refrigerate both pieces 30 minutes.
Make filling: Preheat oven to 425 degrees. Stir together 3/4 cup sugar, the tapioca, and the cinnamon, if desired, in a medium bowl. Put berries, nectarines, and lemon juice in a large bowl. Gently fold the sugar mixture into fruit; let stand 15 minutes.
Pour fruit filling into pie shell, and dot with butter. Cover with remaining dough round. Trim edge of dough flush with top edge of plate; gently press to seal. Crimp edges decoratively; cut steam vents in top crust. Cover edge with a band of foil to prevent excess browning.
Transfer pie to a baking sheet, and bake 35 minutes. Remove foil band, and sprinkle top of pie with remaining teaspoon sugar. Continue baking until filling is bubbling and crust is golden brown, 15 to 20 minutes more.
Let pie cool until warm on a wire rack. Serve with whipped cream, if desired.
If you prefer a buttery piecrust, reduce the amount of shortening by half, and add an equal amount of cold unsalted butter. Cut the butter into bits, and blend it into the dough with the shortening.