Cover a large cutting board with parchment paper and sprinkle cassava flour over the parchment.
Whisk the egg and maple syrup together. Fill a measuring cup with the water.
Whisk together the 1 cup and 2 tablespoons cassava flour, the arrowroot flour and the salt in a large bowl.
Cut the chilled palm shortening into 1/2" pieces and add to the flours. Use your a pastry cutter (recommended) or your fingers to grind the shortening into the flour, breaking it down into smaller bits that are coated in flour. Since it's cold, you might need to use both hands to smoosh down the bigger pieces. You should have pea-sized pieces and smaller bits.
Add the whisked egg and maple syrup and use your hands or a silicone spatula to squeeze and knead the egg mixture into the dough.
Add 2 tablespoons of water and squeeze and knead the dough to incorporate the water. If necessary, keep adding the water, 1 tablespoon at a time, until the dough starts to come together. You're looking for something like play dough but still with just a few crumbs. If it's really sticky, add more cassava and arrowroot, 1 tablespoon each at a time, until it becomes more like play dough.
Plop the dough (technical term) onto the floured parchment and press into a disc roughly 1" thick. Sprinkle on a bit more cassava flour and cover with another layer of parchment. (To wash your hands, use soap and the hottest water you can stand.)
Roll out the dough until it's an approximately 12" circle. Start with the rolling pin in the center of the dough. Pressing gently, roll it away from you, then lift it back to the center to roll it toward yourself, the center and to the left, the center and to the right, and then the center and out diagonally into all 4 corners. Repeat the process until it's the right size.
Carefully peel off the top layer of parchment. With your pie dish nearby, carefully slide your hand under the bottom parchment layer and quickly flip the dough over the pie dish, keeping it centered as much as possible. Carefully peel off the parchment. The dough might crack and break but that's okay! Gently raise the edges and tuck the dough down along the sides into the bottom. Use your fingers to pinch and press together any cracks. If you find that your fingers are sticking to and ripping the dough, fill a glass with warm water and dip your fingers in and then gently dry them so they're just damp.
Pull off any large pieces hanging over the rim of the dish. Use the extra pieces to create a tall, thick layer around the edge of the rim (the dough will shrink a bit as it cools/bakes). You might not need all the dough. If you want, create a fluted edge by using one index finger to press the dough between the index finger and thumb of the other hand.
Chill uncovered for at least 30 minutes and up to 1 day.
Heat the oven to 350°.
Line the crust with parchment paper. Fill the paper with pie weights, dried beans or small dry pasta noodles. Bake for 20 minutes, then remove the weights and paper and bake for another 8-10 minutes, until slightly browned. Cool completely.