Cut very cold butter in until the mixture resembles fine crumbs with a few larger pea-sized pieces.
Mix a couple tablespoons of water with the sour cream and pour it into the dough.
Add a couple more tablespoons of water to the dough and mix until just combined.
Gradually add water, one tablespoon at a time, until the dough just comes together and isn't crumbly. You may not use all the water! Do not over mix!
Divide dough into 2 portions, wrap, and refrigerate until ready to use.
For the Apple Pie
Preheat the oven to 425 degrees and place a baking sheet in the oven to preheat (see note). The pie should be baked on the lowest oven rack.
Peel all the apples. Slice half of the apples 1/3 inch thick and half of the apples 1/4 inch thick.
Combine apples, flour, sugar, lemon juice, lemon zest, spices and salt. Mix until combined.
Roll out one pie crust to about 12 inches in diameter and place it in the bottom of the pie dish. A deep pie dish works best for this recipe. The easiest way to transfer pie dough is to fold it over the rolling pin and gently glide it over the pie dish.
Gently work the pie crust into the pie dish and if there is more than 1-inch excess crust around the edge, trim it to be only 1-inch.
Fill the bottom crust with the apple mixture. You will have to use your hands to wiggle and gently press the apples into the crust. They will be slightly mounded.
Roll out the second pie crust to about 12 inches in diameter. Gently place it over the apples, using the same method detailed in step 9. Trim the edges if you have more than 1-inch excess dough around the edge.
Tuck the edges under and then flute them by placing two fingers from your right hand on the edge of the pie and using your index finger from your left hand to pull the dough between your fingers towards the middle of the pie.
Combine the egg and 1/2 teaspoon of water and brush it gently over the top of the pie.
Cut 4 vents in the top of the pie with a sharp knife.
Sprinkle 1 tablespoon of sugar over the top of the pie.
Place pie on the preheated baking sheet in the oven (line the baking sheet with foil in case the pie leaks for easy clean-up) and bake at 425 for 25 minutes.
Leave the pie in the oven but reduce the oven temperature to 375 degrees and continue baking for an additional 35 minutes until the inside is bubbly and the top crust is dark golden brown. Cover the top of the pie loosely with foil if it becomes browned too quickly.
After pie is finished baking, let it cool completely at room temperature. This allows the pie filling to set up, preventing it from being runny.
You can use any kind of apples you like, but a tart apple like a Granny Smith will hold up better in the oven. I like to combine a tart apple and a sweet apple in my filling. If you have a baking stone, you can bake the pie on the stone instead of preheating a cookie sheet. However, I'd still recommend placing the pie on a baking sheet lined with foil to catch any drips or spills from the filling. The point of baking on a preheated sheet or stone is to apply maximum heat to the bottom crust of the pie so it cooks through.