Start by adding the flour, sugar, and salt into the bowl of a food processor. (If you don't have a food processor, that's okay--you can do this with a pastry cutter.) In a separate, small bowl, whisk together the sour cream and water until smooth and set aside. Sprinkle the small butter pieces evenly over the dry ingredients, then pulse a few times until the butter is the size of peas. 

Add the sour cream mixture into the bowl of the food processor while you pulse a couple of times. Pulse the dough a few more times. To test if the dough is ready, press it together with your fingers. If it sticks together, it's ready. If not, add a tablespoon or two of ice water. It should start to form bigger clumps. 

Dump the dough out onto a well-floured surface and use your hands to press the dough crumbles into a ball. It is going to seem messy, but this just means you're going to have awesome, flaky crust. Wrap the ball in plastic wrap and let it chill for an hour.

Preheat oven to 400 F. 

Mix together the melted butter and sugar and beat with a whisk until a little fluffy. Add the eggs and vanilla and beat until well combined. Add half of the flour and pinch of salt, whisk to combine. Add half of the buttermilk. Repeat using up the rest of the flour and buttermilk. Whisk lightly until smooth. Set aside.

Grab your chilled pie dough from the fridge and roll it out into a 11-12" circle. Place the dough into your pie plate (Use a deep dish 9" plate. 9.5" is fine, too). Press dough into the plate then fold and crimp the edges. 

Pour the filling into the pie shell and put in the oven. Bake at 400 F for ten minutes, then reduce the temperature to 350 F and bake for an additional 40-50 minutes. If you are using a 9.5" plate, check the pie about 30 minutes, as it is probably going to bake faster. The pie is done when the filling is a deep golden brown and a knife inserted into the center comes out clean. Let cool for about an hour and serve warm. Enjoy!