Roll Out the Crust: If the pie dough is cold and firm, let it rest on the counter for about 10-15 minutes before rolling. On a floured work surface, roll out the disc of chilled dough. Turn the dough about a quarter turn after every few rolls until you have a circle that measures 12 inches in diameter.
Carefully transfer the dough to a rimmed baking sheet lined with parchment paper. Cover with plastic wrap and place the crust back in the refrigerator to chill while you preheat the oven and make the filling.
Make the Filling: Preheat the oven to 400°F. In a large bowl, toss together the peaches, sugar, lemon juice, lemon zest, cornstarch, cinnamon, ginger, and salt.
Assemble the Galette: Arrange the filling in the center of the dough, leaving a 1 ½-inch border.
Gently fold the pastry over the fruit, pleating to hold it in.
Brush the crust with egg wash; sprinkle the crust with coarse sugar.
Bake the Galette: Bake in the 400°F oven for 30-35 minutes, or until the filling bubbles and the crust is golden brown.
Warm the jam in a small saucepan over low heat until it’s a nice, thin consistency. Brush the peaches with the jam.
Serve: Cut the galette into 4-6 slices. Top each slice with vanilla ice cream or whipped cream, if desired.