The key to this super-flakey pastry is keeping the dough cold! Be sure to chill adequately between rotations to ensure a workable dough. I also recommend chilling all ingredients before getting started.
In a large bowl, whisk together the brown rice flour, ½ cup of the white rice flour, potato starch, tapioca flour, and xanthan gum. Drop in the margarine by the spoonful. Using clean hands, quickly cut the margarine into the flour until the mixture resembles pebbles.
Add in the cold water and mix quickly to form a slightly sticky dough. Punch down into the bowl to flatten the dough and sprinkle with 2 tablespoons white rice flour; pat into the dough to make it less sticky. Flip and repeat with the additional 2 tablespoons white rice flour.
Chill the dough for 20 minutes in the freezer.
In between two sheets of parchment paper, roll out the dough into a rectangle about 5 × 9 inches. Use a straight edge to square up the edges, forming a solid rectangle. Work quickly so that the dough stays cold!
Fold the dough into thirds (like folding a letter) and rotate a quarter of a turn. Use the parchment to help fold the dough over evenly. Roll it out again into another rectangle 5 × 9 inches. Fold it into thirds once again. Wrap loosely in parchment and chill in the freezer for an additional 20 minutes.
Repeat the steps again, exactly as described above. Wrap and chill the puff pastry until ready to use. When working with the pastry, be sure not to roll it out too thin, ⅓ to ½ of an inch is just right.
Use as directed in recipes calling for puff pastry. To deepen the color of the pastry, mix 2 teaspoons cornstarch with ½ cup water—bring to a boil over medium heat and cook until translucent. Brush a little of the paste onto the surface before baking. Keeps frozen for up to 1 month.
Variation: Easy Puff Cookies
Preheat oven to 400°F. Dust a sheet of parchment with turbinado sugar. Place the puff pastry dough onto the sugared surface and dust with more sugar. Place another sheet of parchment onto the dough and roll out to ⅓ to ½ inch thick. Use a fun cookie cutter to cut out shapes.
Bake on a parchment-covered cookie sheet for about 20 minutes, until golden brown.