6 Tbsp/90 grams unsalted butter, cold
1 cup/134 grams Tara’s gluten-free pastry flour mix (recipe follows)
½ teaspoon xanthan gum
⅛ teaspoon salt (for savory recipes, use 1 ½ times the salt)
⅛ teaspoon baking powder
¼ cup (64 grams) cream cheese, cold
2½ tablespoon ice water
Tara's Gluten-Free Pastry Flour Mix
440 grams white rice flour, as finely-milled as you can get (I use Bob's Red Mill)
154 grams potato starch (not potato flour!)
60 grams tapioca starch (also sold as tapioca flour)
Blend well with a whisk and store in a cool, dry place or refrigerate it.
Cut the butter into small (about ¾-inch) cubes. Wrap it in plastic wrap and freeze it until frozen solid, at least 30 minutes. Place the flour, xanthan gum, salt, and baking powder in a reclosable gallon-size freezer bag and freeze for at least 30 minutes.
Place the flour mixture in a food processor with the metal blade and process for a few seconds to combine. (Depending on the size of your food processor, you may need to make the recipe in two batches if you decide to double it.) Set the plastic bag aside.
Cut the cream cheese into 3 or 4 pieces and add it to the flour. Process for about 20 seconds or until the mixture resembles coarse meal. Add the frozen butter cubes and pulse until none of the butter is larger than the size of a pea. (Toss with a fork to see it better.) Remove the cover and add the water. Pulse until most of the butter is reduced to the size of small peas. The mixture will be in particles and will not hold together. Spoon it into the plastic bag. (If you double the recipe for a double-crust pie, it is easiest to divide the mixture in half at this point.)
Holding the bag closed with one hand, knead the mixture by alternately pressing it, from the outside of the bag, with the knuckles and heels of your hands until the mixture holds together in one piece.
Wrap the dough with plastic wrap, flatten it into a disc (or discs) and refrigerate for at least 45 minutes, preferably overnight.
Dough keeps, refrigerated, for 4 days, or up to 3 months if frozen.
To roll out:
Place the disc of cold dough on a gf flour-dusted board. Dust lightly with additional gf flour, and gently roll it out into the desired shape. If you find the dough to be too sticky, dust the surface and underside with some more gf flour – better to be generous with the flour at this point, and have your dough stay smooth and easy to handle. If it cracks a little, just press it together with your fingertips - don't worry, this dough can handle some wrangling! You’ll find that as the dough warms up under your hands, it becomes more manageable, with even a bit of stretch to it. When it's the right size, gently lift it off the board and ease it into your pie plate/tart pan. (Or, in the case of free-form galettes, onto a parchment-lined baking sheet.) Again, any cracks or breaks can be pushed back together. This dough tastes really good by itself, so when you trim the edges, you may want to save those scraps and bake them off for a little snack. Treat yourself.
Fill and bake according to the directions for whatever recipe you're following (I usually bake at 350ºF for tarts, galettes, and other single-crust items, and 425ºF for double-crust pies), covering the crust with foil midway through baking if it looks like it's getting too dark, too quickly.