I was concerned that my aunts' baking secret had vanished, but thankfully, I uncovered it, and it's more delightful than ever!

In a large bowl, combine flour, sugar, and salt. Add the chilled butter and use a pastry cutter or your fingers to blend until the mixture resembles coarse crumbs.
Gradually add ice water, one tablespoon at a time, mixing until the dough just comes together. Form into a disk, wrap in plastic, and refrigerate for at least 30 minutes.
Preheat your oven to 400°F (200°C).
In a separate bowl, toss the apple slices with lemon juice, brown sugar, cinnamon, nutmeg, and flour until evenly coated.
On a lightly floured surface, roll out the dough into a 12-inch circle. Transfer to a parchment-lined baking sheet.
Arrange the apple slices in the center of the dough, leaving a 2-inch border. Fold the edges of the dough over the apples, pleating as necessary.
Brush the crust with the beaten egg and sprinkle with coarse sugar, if using.
Bake for 35-40 minutes, or until the crust is golden brown and the apples are tender.
Allow to cool slightly before slicing and serving.
Variations & Tips
For a twist, try adding a handful of dried cranberries or raisins to the apple filling for added texture and flavor. You can also experiment with different spices, such as cardamom or ginger, to give the galette a unique taste. If you're short on time, store-bought pie crust can be a convenient substitute for homemade dough. For a nutty crunch, sprinkle some chopped pecans or walnuts over the apples before baking.