1. Place tapioca in a spice or coffee grinder; process until finely ground. Combine tapioca, cherries, and next 5 ingredients (through salt) in a large bowl; toss well. Let cherry mixture stand 30 minutes; stir to combine.
2. Preheat oven to 400°.
3. Roll 1 (9-inch) dough portion into an 11-inch circle. Fit dough into a 9-inch pie plate coated with cooking spray, allowing dough to extend over edge of plate. Spoon cherry mixture and any remaining liquid into dough. Roll remaining (9-inch) dough portion into a 12-inch circle. Cut dough into 12 (1-inch-wide) strips; arrange in a lattice pattern over cherry mixture. Fold edges under; crimp.
4. Combine 2 tablespoons water and egg white in a small bowl. Brush the egg white mixture over dough on top of pie, and sprinkle dough evenly with 2 tablespoons turbinado sugar. Bake at 400° for 20 minutes. Shield edges of piecrust with foil, and bake an additional 40 minutes or until crust is golden brown and filling is thick and bubbly. Cool pie in pan for 45 minutes on a wire rack.
Some pie connoisseurs prefer sour cherries; we love the way sweet ones worked in this filling. A cherry pitter makes quick work of preparing them. We like the OXO Good Grips Cherry Pitter ($12), which also does a good job of pitting olives.