In a bowl, whisk together flour, sugar, and salt, then cut in the cold butter until the mixture resembles coarse crumbs before adding ice water and mixing just until the dough comes together.

Shape the dough into a disc, wrap it, and refrigerate for at least two hours so it firms up and becomes easier to roll.

In another bowl, combine brown sugar, cinnamon, flour, and walnuts, then stir in melted butter until a thick crumble forms and place it in the refrigerator to chill.

Roll out the chilled dough on a floured surface into a large circle, transfer it to a pie dish, trim and shape the edges, brush with egg wash, and chill again.

In a large bowl, mix the apple slices with sugar, flour, lemon juice, spices, and vanilla until evenly coated.

Preheat the oven and place a baking sheet on the lower rack to catch any drips during baking.

Fill the prepared crust with the apple mixture, packing it well so there are no large gaps between slices.

Sprinkle the chilled crumble topping evenly over the apples, covering the entire surface.

Bake at a higher temperature first, then reduce the heat and continue baking until the crust is golden and the filling is bubbling.

Let the pie cool completely at room temperature for several hours so the filling sets properly before slicing.