Prepare the pie crust if you are making homemade pie crust. Refrigerate for several hours or overnight. In a large bowl, mix the blueberries, granulated sugar, lemon juice, tapioca, cinnamon, and nutmeg with a spoon. Set aside.
On a lightly floured work surface, roll out the bottom crust slightly larger in diameter than your baking dish. Gently place the pie crust into the pan lightly, using your fingers. Use kitchen shears to trim the edges of the crust, to about ¾-inch past the pan rim.
Use a slotted spoon to scoop the blueberry filling to the unbaked pie shell. Discard any leftover lemon juice.
Gently cover the entire pie evenly with the crumble topping.
Brush the pie crust edges with an egg wash.
Place in a preheated 400 degree F oven for 1 hour. The crust will be golden brown and the filling bubbling up around edges.
Part way through baking, cover the pie with a piece of aluminum foil you have cut a hole in the center. This will help the pie continue cooking, but let steam escape so your pie crust does not become soggy. This will prevent the edges of the pie crust from becoming too brown.
Let cool for at least an hour or two before slicing. This will allow the pie filling to set.