Combine the Ground Flax with Water in a small bowl, and let sit for 5-10 minutes to thicken.
In the meantime, whisk the Almond Flour, Tapioca Flour, and Salt together in a medium to large bowl.
Add in the thickened Flax, and mix until a dough forms. You can start out mixing with either a spatula or fork, but will eventually need to use your hands. The dough should be damp, but not stick to your fingers (if it is, add in 1 tbsp increments of Almond Flour until the texture is as desired).
Place the ball of dough between 2 sheets of parchment paper, and roll the dough out until it becomes wide enough to cover the base of your pie tin. Peel off the top layer of parchment paper, and gently place your pie tin on top of the dough. Flip the tin over, and remove the other sheet of parchment paper, which should now be on top.
Use your fingers to press the dough evenly into the pie tin (it should be damp, but not sticky). Poke several holes in the dough using a fork. Place the pie tin in the freezer for 20 Minutes; during this time, turn the oven on to 400F.
Cover the dough with Foil and pie weights (or dried beans), then bake for 15 minutes. Uncover, then use the pre-baked pie crust in any recipe of your choosing!
I have not tested this recipe with any other flours, and thus cannot recommend substitutions.
Ground Flax may be substituted with Ground Chia Seeds, but not Whole.
This dough can be made ahead of time and stored in the fridge for up to 3 days prior. I would suggest wrapping it tightly in Syran Wrap, so it does not lose any moisture.