In a food processor blend the flour and salt until combined.
Add cubes of butter and pulse until mixture looks crumbly.
Slowly add in the ice water a tablespoon at a time until the dough begins to form together.
Remove from the food processor, shape into a disc shape, wrap wit plastic wrap and place in the fridge for at least an hour or over night.
Peel apples and cut into 3/4" chunks.
Add apple, butter, brown sugar, pumpkin pie spice, and flour into a dutch over or large pot and cook on medium heat stirring frequently. Simmer for about 30 minutes or until apples are tender. Set aside to cool.
Preheat oven to 400 degrees.
Lightly flour your surface and roll out your pie dough to 14" around. Wrap dough around the rolling pin and place into your pie pan. Crimp the edges with your thumb and fore finger. Place pan into the freezer for 10-15 minutes.
Once oven is preheated remove pie crust from the oven and pie with foil. Use pie weights, dried beans or rice in the center of your crust. Bake for 8 minutes.
Remove the foil and weights and place back into the oven for 5 minutes.
Remove the pie crust from the over and reduce over to 375 degrees.
Pour apple filling into baked pie crust.
Using a food processor pulse the flour, butter, sugar, salt and walnuts in a food processor until incorporated and crumbly. Spoon topping over apple filling.
Bake for 35-45 minutes or until the top is golden brown and filling is bubbling. Remove from the over and cool on a wire rack.
Serve warm with a scoop of ice cream and store covered in the fridge for up to 5 days.