Preheat your oven to 400 degrees Fahrenheit. If your oven runs hot, set it to 375 degrees Fahrenheit. (Use an oven thermometer to ensure the correct temperature)
Remove the chilled pie dough from the fridge and let it sit for about 10 minutes before rolling. Roll out one of the balls of dough into a large circle using a rolling pin. Add a generous amount of flour to the rolling surface and to the rolling pin, to prevent sticking and cracking.
Peel the rolled out dough off the counter surface gently by rolling it backwards onto the rolling pin.
Transfer it to a 9-inch pie plate and gently press the dough into the bottom of the pie plate and over the edges (try for a 1-2 inch overhang if possible).
Add the blueberry filling to the pie crust and smooth out the top.
Repeat the rolling out process with the second ball of dough, this time slicing it into about 10 long, thin slices using a pizza cutter (or a pastry cutter, if you have one).
Create a lattice pattern using the strips of dough, overlapping every second vertical strip with every second horizontal strip.
Trim any dough that hangs over the edge of the pie to 1-2 inches past the edge (try to keep the overhang amount even all the way around). Tuck any overhanging dough under and into the pie plate to create a clean edge.
If your pie plate has a wide edge, seal the edge of the pie by creating a fluted pattern - press into the edge of the pie from the outside with your left thumb and index finger while pressing into the edge of the pie from the inside with your right index finger. Do this all the way around the edge of the pie to create a fluted pattern (and see my tutorial HERE for how to create a beautiful fluted edge to your pies!)
Beat the egg and 1 tablespoon of water and brush it lightly onto the unbaked crust. Use a light hand while brushing - too much egg wash creates an eggy texture after baking.
Dust the crust with the coarse sugar and bake at 400 degrees Fahrenheit for about 10 minutes, and then reduce the heat to 375 (350 if your oven runs hot) and bake for an additional 35-45 minutes or until the crust is evenly browned and the filling is bubbly.
Let the pie cool to room temperature before slicing and serving with whipped cream or ice cream.