Preheat the oven to 350°F. Line a baking sheet with parchment paper.
Prepare the filling. Peel, core, and slice the apples to ¼" thickness.
Add the apples, maple syrup, cinnamon, and salt to a large pot or dutch oven. Cook on medium heat for 5-8 minutes until the apples are softened slightly but still intact.
Add the water and stir in the cornstarch. Increase the heat to high and cook at a rapid boil for 3 minutes.
Spread the apples into a thin layer on a baking sheet and allow to cool to room temperature while you make the crust.
Make the crust. In a large bowl whisk together the oat flour and salt. Add the nut butter and maple syrup and use a fork to incorporate. Add ½ cup of the water and mix until a dough forms. If the dough seems dry, add a few more tablespoons of water - the exact amount of water needed will depend on the absorbency of your oat flour and consistency of your nut butter.
Divide the dough in half. Place the first half of the dough between two sheets of parchment paper and roll to approximately 12" wide.
Place the dough into into a 9" deep dish pie pan. Use a knife to trim the edges straight and use any extra dough to cover any open spots. Prick several times with a fork, then bake for 10-12 minutes.
Take the other half of the dough and place it between two sheets of parchment paper. Roll to approximately 12" wide. Then using a sharp knife or pizza dough cutter, slice into ¾" wide strips.
Shape the strips into a 10"-11" lattice, with the open spaces approximately ¾" apart. Press down gently on the places where the crust overlaps to seal the layers together. Set aside. *See post for detailed lattice instructions.
Pour the cooled apple filling into the baked bottom crust. Press as many apples as you can into the crust, without overfilling. Be sure to scoop any extra liquid from the tray into the pie, even if you don't use all the apples.
Transfer the lattice to the top of the pie. Press the edges down to meet the crust. Then use a knife to trim off the edges.
Make an egg wash by mixing the agave and soy milk.
Brush the top of the pie with the egg wash then sprinkle generously with the turbinado sugar (optional).
Bake for 45-50 minutes until the topping is golden and the inside is starting to bubble. Remove from the oven and let cool. For best results let the pie cool completely. Apple pie is more hearty than other fruit pies and can be served after just a couple hours of cooling.
Once completely cool, use a sharp knife to slice. Serve with a drizzle of vegan caramel, a topping of whipped cream, and/or a scoop of vegan vanilla ice cream if desired. Enjoy!