Prepare the Galette Dough:

1. Make the Dough: In a large bowl, combine the flour, salt, granulated sugar, ground ginger, cinnamon, and nutmeg.
2. Cut in Butter: Add the cold cubed butter and use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs.
3. Add Water: Gradually add cold water, one tablespoon at a time, mixing until the dough comes together. Form it into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Prepare the Apple Filling:

1. Mix Apples: In a large bowl, combine the sliced apples, brown sugar, lemon juice, ground ginger, cinnamon, nutmeg, flour, and salt. Toss to coat the apples evenly and set aside.

Assemble the Galette:

1. Preheat Oven: Preheat your oven to 400°F (200°C).
2. Roll Out Dough: On a lightly floured surface, roll out the chilled dough into a rough circle about 12 inches in diameter.
3. Transfer to Baking Sheet: Place the rolled dough onto a parchment-lined baking sheet.
4. Add Filling: Spoon the apple mixture into the center of the dough, leaving a 2-inch border around the edges.
5. Fold Edges: Gently fold the edges of the dough over the apples, pleating as you go to create a rustic look.
6. Egg Wash: Brush the exposed dough with the beaten egg and sprinkle with coarse sugar.

Bake:

1. Bake Galette: Bake in the preheated oven for 30-35 minutes or until the apples are tender and the crust is golden brown.

Serve:

• Let the galette cool for a few minutes before slicing. Serve warm or at room temperature, optionally with a scoop of vanilla ice cream or whipped cream.