Whisk together the flour, salt and baking powder in a large bowl.
Add the cubed butter to the bowl and use your fingers to work the butter into the flour until the mixture is the consistency of wet sand.
Stir in the sour cream (the dough will be very wet), and then turn the dough out onto a well-floured work surface.
Knead the dough a few times until it comes together, adding more flour, 1 teaspoon at a time, if the dough is too sticky to handle. Roll the dough into an 8x10-inch rectangle and dust both sides with flour before folding it into thirds as if you were folding a letter.
Rotate the dough 90º and roll it out again into an 8x10-inch rectangle. Fold the dough again into thirds then shape it roughly into a disk. Wrap it securely in plastic wrap and refrigerate it for at least 30 minutes and up to overnight.
Preheat the oven to 425°F.
Flour your work surface then unwrap the dough and roll it into an 11- or 12-inch circle (depending on the lip of your pie plate).
Transfer the pie crust into a 9-inch pie plate. Crimp the sides into your desired design.
Refrigerate the pie crust for 20 minutes or place in freezer for 5 minutes before baking.
Proceed with the pie per your recipe’s instructions. If your dough requires par-baking, see my notes below.