01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing some to hang over the edges for easy removal.
02 - In a large mixing bowl, cream together butter and granulated sugar until pale and fluffy. Add flour and salt, and mix until a soft dough is formed.
03 - Press the dough evenly into the bottom of the prepared pan. Bake for 15 minutes, until slightly golden. Remove and let rest.
04 - Combine diced apples, brown sugar, flour, cinnamon, nutmeg, and lemon juice in a bowl, tossing until well coated. Layer apple mixture evenly over the warm crust.
05 - In a medium bowl, whisk together flour, brown sugar, granulated sugar, cinnamon, and salt. Add cold cubed butter and cut in using a pastry cutter or fork until mixture forms coarse crumbs.
06 - Sprinkle crumb topping evenly over apples. Return pan to oven and bake for 30 minutes, or until the topping is golden and apples are tender.
07 - Allow dessert to cool completely in the pan. Lift out carefully using the parchment paper overhang and slice into squares.