Make the crust. Combine the flour, sugar, and cubed butter in a large bowl. Drizzle in the water and smash the butter into pea-sized crumbs using a pastry cutter, fork, or fingers. Then, work the dough to form a ball. If the dough is very dry, add in more water. You want to create a loose ball and flatten it into a disc shape. Work quickly to avoid melting the butter with your hands. Wrap the dough in plastic wrap and let the dough chill for an hour.
While the dough is chilling, prepare the apples. Slice and core the apples. Slice the apples into thin slices, about ⅛-inch in size. Keep the apples together in sections. Set the side.
In a small bowl, combine the cinnamon, ginger, and nutmeg. Set to the side.
Preheat the oven to 425 and prepare a baking sheet with parchment paper. Set to the side.
Prepare a surface with flour or parchment, and get ready to roll out the dough. Use a rolling pin to roll the dough to about ¼-inch thick. The dough does not have to be in a perfect circle; it should aim for an even thickness. If you want even edges, use a pie or pizza cutter to slice off the edges for an even cut.
Place the apples in the middle of the crust and work your way out to cover most of the area. Leave about 2-3 inches from the apples to the border of the crust. Then, sprinkle the apples with the cinnamon mixture and top with the cold cubes of butter.
Fold the crust over the apples, overlapping the edges as you go. Brush the edges with eggwash and top with the coarse sugar, if desired.
Bake the galette for 25-30 minutes. Look for a golden brown crust and soft apples to know when the galette is done.
Let the galette cool for about 10 minutes after it comes out of the oven so that all the juices will not run out when cut.
