Mix the ground flax with the water in a small bowl. Let it sit for 5 minutes until it thickens into a gel.
Whisk together the almond flour, tapioca flour, and salt.
Add the flax egg (plus vanilla and maple syrup, if using). Mix until a dough forms.
Add water a little at a time until the dough is malleable enough to mold and holds together without cracking, but is not wet or sticky.
Press the dough evenly into a pie pan.
Bake at 350°F until golden, about 12 to 15 minutes, before adding your filling.
