1. In a food processor, combine flour, sugar, and salt. Add cold butter and pulse until coarse crumbs form. Gradually add ice water until dough comes together. Divide into 2 discs, wrap in plastic, refrigerate at least 1 hour.

2. In a large bowl, toss apple slices with granulated sugar, brown sugar, cinnamon, nutmeg, allspice, flour, lemon juice, and vanilla until evenly coated.

3. Preheat oven to 375°F (190°C). Roll one dough disc into a rectangle slightly larger than a 9×13 inch baking sheet. Place on parchment-lined baking sheet. Spread apple filling evenly, leaving border around edges. Roll second dough disc, place over apples. Trim edges, crimp to seal, cut slits for steam. Brush with egg wash and sprinkle sugar if desired.

4. Bake 45–55 minutes until crust is golden and filling bubbles. Cool slightly before slicing into squares.