Add flour(s), sugar, and salt to the food processor. Pulse until mixed. Open the lid and scatter the butter over the dry ingredients. Pulse about 7-8 times. Open and drizzle 3/4 of the water/vinegar over the mixture and cover. Pulse again until the mixture resembles coarse crumbs, about 5-6 times. Avoid the dough balling around the blades. Squeeze the dough between your fingers. If the dough seems dry, slowly add more water and pulse 1-2 more times. Depending on season and outside temperature, you may or may not use all of the water.
Pour the dough mixture onto your work surface. Ball the dough, then flatten into a 3/4-inch disk and wrap. Refrigerate for at least an hour or overnight.
Sour Cream Apple Filling
In a large bowl, whisk sour cream, sugar, egg, flour, salt, vanilla, cinnamon and nutmeg until even mixed. Add the apples; mix until combined, then let stand on the counter for 30-45 minutes.
Preheat the oven to 400 degrees F. Once dough is ready to roll, lightly flour your worksurface and rolling pin. Starting in the center, apply decent pressure and roll the dough into a 13” circle. To avoid sticking rotate the dough every few rolls. If necessary, lightly re-flour underneath the pie dough. Transfer the dough to a 9½-inch pie pan. Let the pastry fall into the pan. Trim the edges to 1/2-inch beyond the pie pan and crimp/flute the edge. Crack and separate an egg white. Brush the bottom to midway up the side; this helps seal the crust and prevent a soggy bottom. Place the pie pan in the refrigerator.
Take the shell from the refrigerator and layer the apples and juices into the pie pan, rather than pouring and mounding in the center. For overall look and an even bake, we want to avoid vacant and areas of void as the apples further soften under heat. Spatula remaining sour cream spice liquid in the pie and give the apples one final gentle but firm press.
Bake on center rack for 15 minutes.
After 15 minutes, reduce the temperature from 400° to 350° and bake for another 30 minutes.
Meanwhile, make the streusel topping. Combine the flour, sugar, cinnamon, salt, and walnuts in a medium bowl. Drizzle the melted butter and stir with a fork, then spatula or your hands until the mixture is a mix of small to medium crumbs. Refrigerate until ready for use.
After 30 minutes total, remove the pie from the oven and streusel from the refrigerator. Remember which side of the pie was facing front, as we are going to place that towards the back when returning to the oven. While adding the streusel, use your hands to break then squeeze the crumbs into varying sizes while adding to the pie. Once finished adding, give another gentle press. Place a pie shield or foil around edges to prevent over browning, slide a pan one rack below, and rotate the pie 180°. Continue baking for another 20 minutes, or until the top is toasty golden and a butter knife slides with ease through the inside apples.
Once pie finishes baking, transfer to a wire rack. Let cool for at least three hours or overnight. Slice and be one with the beauty you created.
Notes
Pie adapted from Pie the best Pie Guy of all ; ) Crust
if dough is in the refrigerator for over an hour, let stand for 5 to 10 minutes before rolling.
the dough can be frozen for up to one month.
why place the pie in the refrigerator prior to baking? By firming an all butter crust, the edge keeps form better throughout the baking process.
Streusel
for a crunchier top, use melted butter. For a less crunchy streusel, cut cold to room temperature butter into the flour/sugar/spice mixture. Your pie, your streusel, your design =D