Whisk the flour, sugar, and salt together in a medium bowl. Using a pastry cutter or 2 forks, cut in the butter until the mixture resembles coarse pea-sized crumbs. Add the water and stir until the flour is moistened. Add 1–2 more Tablespoons of water if the dough seems dry. Turn the dough out onto a lightly floured work surface and, using your hands, work the dough into a ball. Flatten it into a thick disc. Wrap the dough disc in plastic wrap or parchment paper and refrigerate it for at least 1 hour, and up to 3 days.

Mix the apples, brown sugar, flour, lemon juice, cinnamon, and nutmeg together in a large bowl. Cover tightly and let sit until the dough is ready. I usually cover it and keep it in the refrigerator during this time.

Line a large baking sheet with parchment paper or a silicone baking mat. Clear some shelf space in your refrigerator because the shaped galette must chill in step 6. (See recipe Note below.)

On a lightly floured surface, roll the dough into a 12-inch circle—it doesn’t have to be perfect. Transfer dough to the prepared baking sheet. (You can also roll the dough out right on the parchment paper or silicone baking mat that you are using to line the baking pan. If doing so, lightly flour the parchment paper or baking mat.)

Arrange the apples (and any juices from the bottom of the bowl) into the center of the dough, leaving a 2–3-inch border all around them. You can simply spoon the filling on, or arrange the apple slices in a more deliberate design, such as concentric circles. Gently fold the edges of the dough over the filling, overlapping the dough as necessary. Press gently to seal the edges. Brush the crust edges generously with egg wash and sprinkle the crust with coarse sugar, if desired. If desired, drizzle 3 Tablespoons of salted caramel over the filling (not the crust).

Refrigerate the shaped galette for at least 15–20 minutes as the oven preheats (next step), and up to 8 hours. If refrigerating for longer than 1–2 hours, cover it lightly. The galette will lose its shape if it’s not cold when it hits the oven.

Preheat oven to 400°F (204°C).

Bake until the filling is bubbly and the crust is golden brown, about 35–36 minutes. Remove from the oven and allow to cool on the baking sheet for 10 minutes before slicing and serving. If desired, serve with vanilla ice cream and more salted caramel sauce drizzled on top.

Cover and store leftover galette in the refrigerator for up to 4 days.