Make the crust. Combine the flour, sugar, and salt. Stir together. Cut in the butter a tablespoon at a time. Coat the butter in the flour. Using your hands, snap/rub the butter chunks between your thumbs and opposing other fingers to create shreds. Do this until all the butter has been handled. The mixture will look coarse and crumbly. Add water one tablespoon at a time until the mixture just comes together. I prefer to continue working with my hands here, but feel free to grab an oversized fork. Press the dough together to make a disk. Crumbs are common. Cut the disk in half. Place the crumbs on top of one side then place the remaining disk on top of that. Press out. Do this a couple more times to create both layers an incorporate all the crumbs. Wrap disk in plastic wrap and place in the fridge to rest.
Meanwhile, prepare the apples. Peel, core, and thinly slice the apples (a tiny bit thicker than a mandolin). Into a bowl, add the apples and spices, and gently stir together. Set aside. Preheat the oven to 375°F. Line a baking sheet with parchment paper. Set aside. Pull out the chilled dough. On a lightly floured work surface, roll out the dough until about 10” in diameter. If the dough sticks at all, add a bit more flour. Fold the dough into quarters and transfer to the parchment-lined baking sheet. Unfold. Add apples in a decorative pattern, or pour all at once to the middle of the dough, being sure to leave about 1.5” clearing from the edge. Fold the dough over the apples. Paint the edges with the egg wash. Sprinkle with coarse sugar. Pour any remaining juices from the apple bowl into the middle of the galette. Bake for about 30 minutes. To get that deep golden crust, turn the oven to broil in the last minute of baking. Watch closely. Remove and allow to cool for 15-20 minutes before serving.