First, make the pie crust. In a large bowl, combine the flour, sugar, and salt. Add the cold butter. Using a pastry blender or two forks, cut the butter into the flour mixture until it resembles coarse meal and the biggest pieces of butter are the size of peas. Add in the cold water, 1 tablespoon at a time, and stir with a spoon until the dough just comes together. It will still be clumpy. Knead the dough with your hands, until it forms a dough ball. The dough shouldn't be sticky. Wrap the dough in plastic wrap and flatten into a disc. Refrigerate the dough for one hour or up to three days. You can also freeze the dough for up to 1 month. Place the plastic-wrapped dough into a freezer bag. To defrost, remove from the freezer and place in the refrigerator for one day to thaw.
While the pie dough is chilling, make the crumb topping. In a medium bowl, combine the flour, oats, brown sugar, granulated sugar, and cinnamon. Stir together with a whisk. Mix in the butter with your fingers until the mixture comes together and you have big crumbles. Place in the refrigerator while you make the apple filling.
To make the apple filling, place the apples, lemon juice, sugar, flour, vanilla, cinnamon, and allspice in a large bowl. Stir gently until apples are coated. Set aside.
Preheat oven to 375 degrees F. Get out a 10x15 inch jelly roll pan. To assemble the pie, remove the crust from the fridge. On a lightly floured surface, roll the pie dough into a big rectangle, about 18x13 inch size. Try to work quickly so the dough doesn't get too warm. Carefully transfer the dough to the jelly roll pan. Trim the dough that is overhanging the sides to 1-inch. Smooth the dough so it fits into the edges and corners.
Pour the apple filling over the dough and spread evenly with a spatula.
Remove the crumb topping from the fridge. Sprinkle evenly over the pie. Pinch or crimp the excess pie dough on the sides and edges.
Bake for 40-45 minutes or until the crust is golden brown and the apple filling is slightly bubbling. Remove from oven and place on a wire cooling rack. Cool until room temperature. Cut into pieces and serve!
Note-this pie is good served warm, at room temperature, or even cold. I like it with vanilla ice cream:) It will keep covered in the fridge for 3-4 days. It can be made in advance! YAY!