Preheat the Oven: Preheat your oven to a toasty 350 degrees Fahrenheit.
Prepare the Crust: In a large bowl, blend flour, brown sugar, cold butter, and oats using a pastry blender. Set aside one cup of this delightful mixture for the crumb topping. Press the remaining mixture into a 9-inch pie pan, creating the foundation for your soon-to-be masterpiece.
Create the Filling: In a saucepan, combine sugar, cornstarch, and water over medium-high heat. Let it boil and cook for 2 minutes, whisking continuously to achieve a thick, luxurious consistency. Remove from heat and gently fold in the peeled, sliced Granny Smith apples, vanilla, cinnamon, nutmeg, ginger, and allspice.
Assemble and Bake: Pour this flavorful apple mixture into the prepared crust, ensuring an even distribution. Sprinkle the reserved crumb topping generously over the apples. Now, into the preheated oven, it goes! Bake for 40-50 minutes until the crumb topping takes on a golden hue and the apples beneath are tender.
Cool Before Serving: Patience is a virtue, especially when letting this delectable Dutch Apple Pie cool before serving. The wait will be worth it.