Step 1

Place a baking sheet on the middle rack of the oven and preheat to 400 degrees F.

Step 2

Roll 1 pie dough into a 12-inch round and fit it into a 9-inch pie plate, leaving an overhang for now. Place the dough into the refrigerator while you make the filling.

Step 3

Mix the blueberries, sugar, tapioca, lemon zest and juice and salt in a large bowl until well combined. Remove the pie plate from the refrigerator and fill with the berry mixture. Dot the top of the pie with the butter. Top with the remaining pie dough, pressing around edge to adhere, and trim to a 1/2-inch overhang. Crimp the edge, then cut five vents in the center of the pie with a paring knife. Mix the egg with 1 tablespoon water, then brush the pie with the egg wash.

Step 4

Place the pie plate on the preheated baking sheet and bake for 20 minutes. Reduce the temperature to 350 degrees F and continue baking until the crust is golden brown and the filling is bubbling and the berries are beginning to burst, 30 to 35 minutes more. Let the pie cool completely on a wire rack, about 2 hours.