Start by making the crumble topping. Combine the flour, brown sugar, and warming spices in a bowl, mixing until evenly combined. Add the cold, cubed butter and gently rub it in with your fingers until the mixture resembles coarse sand with little buttery pieces. If your kitchen is warm, pop it in the fridge for a few minutes so it stays firm and bakes up perfectly crisp. Keep it chilled while you prep the apples.
Peel, core, and thinly slice your apples, about an eighth of an inch thick works best. I love using a mix of Granny Smith and Honeycrisp for that ideal balance of tangy and sweet. Toss the slices immediately with lemon juice. Then sprinkle in the brown sugar, granulated sugar, vanilla extract, cinnamon, nutmeg, cornstarch, and salt. Gently fold everything together so each slice is coated evenly.
Fit your store-bought pie crust into the pan and press it lightly into the edges. Add the apple mixture, layering and tucking slices so the filling is full but airy. Spread your chilled crumble evenly over the top, making sure to cover every corner.
Preheat your oven to 390°F (200°C) and bake the pie for 10 minutes to give the crust a head start. Lower the temperature to 375°F (190°C) and continue baking for 40–45 minutes, until the topping browns and the apples release bubbling juices.
Once it’s done, let the pie cool for at least 30 minutes before slicing. Waiting a bit allows the filling to set, so you’ll get clean, perfect slices.