Pour the filling into the unbaked pie shell and dot with the knob of butter, cut into pieces. It’s okay to tear pieces off with your fingers as well.
Roll out the remaining disc of dough, lay it over the fruit, and cut 5-6 vents on top, or cut strips and make a lattice top. Trim excess dough from the edges and crimp.
Lightly brush some of the egg wash over the entire pie, including the edges.
Bake for 20 minutes at 425°F (220°C).
Reduce the heat to 350°F (175°C) and bake for 30-35 minutes more.
When there are about 10 minutes of bake time left, open the oven, pull the pie out, and quickly and even sprinkle the top of the pie with sugar.
If the filling is not making steady bubbles, turn the heat back up to 450°F (230°C) for 5 minutes to help it along.
If needed, cover the pie loosely with a vented piece of aluminum foil, shiny side down, before you turn the heat up.
Remove the pie from oven and cool as long as you can before serving, so the filling can set up.