Prebake the crust. Press your pie crust into a 9" deep dish pan. Prick the crust with a fork and place it in the fridge for 30 minutes. Preheat oven to 350°F. Remove the pie pan from the fridge, and loosely cover the top with foil or parchment paper. Fill with pie weights or beans. Bake for 25 minutes. Set crust aside and allow it to cool for 10 minutes.
Prepare the filling. Meanwhile, combine all filling ingredients except apples in a large mixing bowl and stir until they are well mixed. Add apples (2 pounds) and toss until filling is evenly distributed. Pour into the cooled crust.
Prepare the topping. Combine flour (1/2 cup), sugar (1/3 cup brown sugar & 1/3 sugar), and cinnamon (1 tablespoon) in a medium bowl and mix well. Blend in butter (1/2 cup) using 2 knives or a pastry blender, until the mixture is crumbly. Toss in the walnuts (1 cup) until coated. Sprinkle crumble topping over the filling.
Bake. Place pie on a cookie sheet and loosely cover with aluminum foil. Bake in the preheated oven, loosely covered for about 1 hour and 10 minutes. Uncover and continue to cook until about 10-15 minutes until the filling is set, slightly puffed, and lightly golden.
Sour Cream: I use full-fat sour cream in this recipe. I love the creamy richness it adds.
Foil: While not an ingredient, the foil does serve to protect. The streusel and pie crust can over brown without it.
Apples: The star of the pie, apples come in a ton of varieties. Here's a list of the best ones to choose for pie. I opt for granny smith since they hold their shape in baking and give you a strong apple flavor even when cooked.
Blind Baking: This is also known as prebaking. This is done to keep the crust crispy. Without doing this, the moisture from the custard will produce a soggy crust. To blind bake, poke the bottom of the crust with a fork (so it doesn't puff up during baking), place a piece of parchment paper loosely over the crust, then line the crust with pie weight or dried beans. Bake as instructed in the recipe below, remove the parchment paper, pie weight, or beans.