You can mix by hand or with a standing mixer. Combine the brown rice flour, potato starch, tapioca flour, sugar, and salt. Mix to combine.
Add the coconut oil. If it's a hot day and the coconut oil is liquid, put it in the refrigerator until it solidifies. It won’t work very well in the recipe if it's not solid.
Add the egg and water and mix on medium-low until fully combined and the dough starts to come together.
Turn off the mixer, and gather the dough with your hands into a ball. It’s not necessary to chill the dough. It's actually kind of hard to work with when its cold
With your palms, press the dough into a flat disc.
Place the dough between two pieces of waxed paper, and with a rolling pin, roll it into approximately a 12-inch disc.
Remove the top piece of wax paper. Put the pie plate, open side down on top of the dough and carefully invert the dough into the pie pan.