How to Make It
In a food processor, combine the rice flour, potato starch and xanthan gum and pulse until well mixed. Add the butter and pulse until coarse crumbs form. Add the egg and 2 tablespoons of the ice water. Pulse a few more times until the dough clumps together. If necessary, add up to 2 tablespoons more ice water, 1 tablespoon at a time.
Transfer the dough to a work surface and form it into a flat disk. Wrap in plastic and refrigerate for at least 1 hour.
Remove the dough from the fridge and let stand at room temperature for 10 minutes. Place it on a work surface covered with a lightly floured sheet of parchment paper. Dust the dough with rice flour and cover with another sheet of parchment. Roll out the dough to a 12-inch round. Peel off the paper and fit the dough into a 9 1/2-inch tart or pie pan. Patch any holes with excess dough.
To bake, preheat the oven to 350°. Fill the pie with the fruit of your choice and bake for 30 to 40 minutes, until the fruit is caramelized and the crust is golden brown.