Roll the pie dough out into a large circle on a floured surface to about 12- to 13-inches in diameter and 1/8-inch thick. Place on parchment on a baking sheet and arrange the apples and squash slightly mounded in the center leaving a two-inch border around the edges. Fold in edges overlapping as you tuck and turn the galette.
Preheat oven to 350°F, placing a rack in the center of the oven. Bake the galette 30 minutes, brush edges with egg wash and bake 15-25 minutes more until crust is deep golden.