Preheat oven to 425 F. Combine 4+ cups of pitted sour cherries (I prefer the bright red Montmorency cherries), 3 TBL minute tapioca, ¾ cup sugar and 2 TBL kirsch. Let stand 15 minutes. Meanwhile, roll out pie crust and fit into 9-inch pie plate. Pour filling into crust, dot with 2 TBL butter cut into small pieces, cover with top crust and seal. Brush top with egg white.
Bake 10 minutes. Reduce heat to 350 and continue baking until crust is golden brown, about 35 to 40 minutes more.