Toss together the berries, sugar, cornstarch, nutmeg, freshly grated ginger, lemon zest, and lemon juice in a large bowl.
Roll out the second disk of dough to 1/8-inch thick and use a pastry cutter to make strips for the lattice top.
Pour the blueberry mixture into the chilled pie shell. Lay out strips of dough over the blueberries, about 1/2-inch apart. Fold every other strip in half and lay more strips across the ones that are not folded. Unfold the first strips over the ones you just put down. Repeat this, but alternate which strips you fold, until the whole blueberry pie is covered.
Fold the bottom crust over the lattice top, trimming any extra so it isn't too bulky.
Crimp a design into the edge. If the dough has gotten very soft while working, place it in the freezer for a few minutes before baking.
Brush the top of the blueberry pie with egg wash and place the butter between the lattice work. Sprinkle with sugar. Place the pie on a baking sheet in case the juices from the pie bubble over the edge of the pie place and slip it into the oven.
Bake for 20 minutes and then drop the temperature to 400°F and continue baking for about 40 or until the crust is golden brown and the filling is bubbling. If the crust is nicely colored, but the filling isn't bubbling, tent the pie with foil.
Allow the blueberry pie to cool to room temperature and serve with ice cream or whipped cream.