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1
Whisk white rice flour, cornstarch, tapioca flour, coconut flour, sugar, salt, and xanthan gum together in a medium bowl. Cut butter into 1/2-inch cubes and toss with flour mixture to break up the pieces. With your fingertips, smash each cube into a thin sheet-that's it! Stir in water, then knead dough against the sides of the bowl until it comes together in a shaggy ball.
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2
On a very generously dusted work surface, gently roll dough into a roughly 10- by 15-inch rectangle, sprinkling more cornstarch above and below to prevent sticking. Don't be shy! Fold the 10-inch sides to the center, then close the newly formed packet like a book. Fold in half once more, bringing the short sides together to create a thick block. The dough will crack along the creases, but that's just fine. Divide in half with a sharp knife or bench scraper. If dough is very soft or if you are working in a hot kitchen, refrigerate for 15 minutes before continuing.
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3
Using as much cornstarch as needed, gently roll one piece into a 12-inch circle. Slide an offset spatula underneath it to loosen, then divide into quarters. Transfer to the pie plate one at a time, folding the top edge of each piece over to create a thick border that sits atop the rim of the pan. Press and pinch dough together along the seams to form a unified whole. Repeat with remaining dough. Wrap with plastic and refrigerate at least 2 hours and up to overnight. Use as directed in your favorite recipe.
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4
Shape one piece of dough according to the directions above. For a solid top crust, roll remaining dough the same way, or roll into a 9- by 15-inch rectangle for a lattice-top pie. Divide into manageable pieces and transfer to a baking sheet or parchment-lined cutting board. (The parchment will prevent dough from absorbing any savory odors from the board.) Wrap both portions in plastic and refrigerate at least 2 hours and up to overnight. Use as directed in your favorite recipe.
