This recipe which is good for sweet or savoury pies is from She Knows and original recipe from Savory Pies by Greg Henry.
Gluten-Free Pie Pastry
Yields 2 (8-inch) pie crusts or 1 (8- to 10-inch) double-crust shell
2 cups millet flour
1/4 cup tapioca flour
1/4 cup potato starch, plus more as needed
1 teaspoon salt
2 teaspoons lemon juice or white vinegar
2 sticks (1 cup) very cold European-style unsalted butter, cut into 1/2-inch dice
1 egg replacer (as per packet instructions)
2 tablespoons water, or more as needed
In the bowl of a food processor, pulse the flours, potato starch and salt 5 to 6 times until well combined.
Add lemon juice or vinegar and butter. Process 6 to 8 seconds until crumbly and coarse, with various-size chunks of butter visible throughout.
Add egg replacer and 2 tablespoons water. Run machine until the dough comes together and begins to pull away cleanly from the sides of the bowl, 15 to 20 seconds. Add water as needed.
On a work surface lightly floured with potato starch, gently knead the dough 2 to 3 times. If it seems sticky, sprinkle in a few teaspoons of potato starch and give it a couple more quick, gentle kneads.
Divide in half and shape into 2 discs about 5 inches in diameter and 3/4-inch thick.