In a large mixing bowl, combine the gluten-free flour blend, xanthan gum, baking powder, and kosher salt. Whisk until well-combined.

Add the chilled, chopped butter to the dry mixture. Toss and coat the butter with flour, then flatten each chunk of butter with your fingers.

Create a well in the center and add the sour cream. Mix gently until moistened; the dough should appear shaggy.

Isolate dry patches, drizzle with ice water, and knead lightly until the dough comes together.

Press the dough into a disk shape, wrap in plastic wrap, and refrigerate for 30 minutes.

On a floured surface, roll the chilled dough into a rectangle about 1 inch thick, then fold into thirds like a letter.

Repeat the rolling and folding process two more times to create layers.

If dough feels warm, chill until firm. Roll out to an 11-inch round, 3/8-inch thick, pinching any splits.

Transfer to a greased 9-inch metal pie plate and crimp the edges.

Cover with plastic wrap and chill in the refrigerator for at least 30 minutes.

Preheat your oven to 375°F. Pierce the bottom with a fork, cover with parchment paper, and fill with pie weights.

Bake for about 10 minutes until edges are slightly golden.

Remove the weights and brush the bottom with egg white if shiny. Bake for another 2-4 minutes until lightly golden.

Allow the crust to cool completely before filling.