In a large mixing bowl, combine the gluten-free flour blend, granulated sugar, salt, and baking powder. Stir until well mixed.
Add the cold, cubed unsalted butter to the flour mixture. Using a pastry cutter or your fingers, work the butter into the flour until the butter is coated in the flour and there are some larger pieces of butter remaining, about the size of an almond.
Gently mix in the cold sour cream until the dough starts to come together. The dough will be shaggy and slightly dry at this stage.
Knead the dough in the bowl until it forms a ball. This can take a few minutes to do. At first the dough will be dry, but as you knead it the flour will hydrate with the sour cream and some of the butter will melt from the warmth of your hands to form into a ball.
Shape the dough into a rectangular block and wrap it tightly in plastic wrap. Refrigerate for about 30 minutes to allow the butter to chill.
After chilling, unwrap the dough and place it on a lightly floured surface. Roll the dough out into a long rectangle, about 1/4 inch thick.
Fold the dough into thirds, like folding a letter, by bringing one short side of the dough over the center, then folding the other side over that. Rotate the dough 90 degrees and roll it out again into a large rectangle. Do the folding and rotating process 4 times in total. This creates multiple layers of butter within the dough, resulting in a flaky crust.
Divide the dough into two portions. Shape each portion into a disk and wrap individually in plastic wrap. Refrigerate for at least 1 hour before using. If refrigerating for longer than an hour, let the dough soften at room temperature for about 15 minutes before rolling it out.
Use this gluten-free pie crust in your favorite pie recipe!