Heat oven to 375° F.
Gently roll out crust on a floured surface to a 12-inch round. Fit into a 9-inch deep-dish pie plate and flute edge. Refrigerate until ready to fill.
Melt 2 tablespoons of butter in a large nonstick skillet over medium heat. Add apples and 1/2 cup of the granulated sugar. Cook, stirring frequently, 12 to 15 minutes until barely tender. Let cool on rack.
Make streusel: Combine pecans, brown sugar, 1/2 cup of the flour, the cinnamon and 1/8 teaspoon of the salt. Cut up the 6 tablespoons cold unsalted butter; rub into mixture until crumbly.
Mix remaining 1/2 cup granulated sugar, 1/4 cup flour and 1/8 teaspoon salt. Stir in sour cream, vanilla, egg and nutmeg. Fold in apples. Pour into prepared crust. Top with streusel and place on a baking sheet.
Bake at 375° F for 60 minutes until apples are tender; tent with foil after 30 minutes. Cool 4 hours and serve.
Make sure filling is at room temperature and crust well chilled or bottom crust will be soggy.