In a large bowl, combine the flour, white sugar, and salt. Grate in the cold unsalted butter using a cheese grater, working in batches to prevent the butter from softening—if needed, chill the butter between grating. Toss the grated butter into the flour mixture as you go. (Alternatively, cube or slice the butter and cut it in using a pastry blender or two forks.) Create a well in the center and add 1/2 cup ice-cold water, mixing quickly with a fork. Drizzle in extra cold water, 2 tablespoons at a time, until the dough just holds together and isn’t sticky. You should still see small pieces of butter throughout the dough, which is key for flakiness.

Turn the dough onto a lightly floured work surface and knead quickly and gently to bring it together. Divide the dough in half and flatten each half into a 1-inch thick rectangle. Wrap each piece in plastic wrap and chill in the refrigerator for at least 30 minutes. I always chill my pie dough to help relax the gluten and keep the layers super flaky.

Preheat your oven to 400°F. Lightly dust your work surface with flour, then roll out one dough rectangle to fit a 9x13-inch jelly roll pan. Press the rolled dough into the bottom of the pan. Spread the prepared apple pie filling evenly over the crust. Roll out the second dough rectangle and place it on top of the filling. You may use a rolling pin to help transfer the dough. Pinch the edges together lightly, and cut a few vents in the top crust to allow steam to escape.

Bake the assembled pie in the preheated oven for about 40 minutes, rotating the pan halfway through baking, until the crust is golden brown. Once baked, remove the pie from the oven and place it on a wire rack to cool completely before glazing.

Beat the confectioners’ sugar, room temperature butter, vanilla extract, and whole milk together in a bowl until smooth and creamy. Once the pie has cooled, spread the glaze evenly over the top crust. Allow the glaze to set and harden. Then, slice the pie into squares and serve. For a little extra flavor, I sometimes add a pinch of cinnamon or a squeeze of lemon juice to the glaze.