For the crust, toss the flours, salt, and butter into a medium bowl, and combine them with a fork or pastry cutter. Alternately, this may be done in a food processor, pulsing to roughly incorporate. Continue blending until coarse crumbs develop and small pieces of butter are left intact. Mix in the maple syrup, followed by the water, adding just one tablespoon at a time until the dough comes together into a cohesive ball. You may need to work the dough with your hands as it becomes stiff. Divide the resulting dough into two even pieces, smooth them into round disks, and wrap each tightly with plastic wrap. Refrigerate the dough for at least 2 hours before proceeding.

Once the dough is thoroughly chilled, preheat your oven to 400ºF (205ºC). Take one of the disks and roll it out to about a ¼-inch thickness on a lightly floured surface. Carefully move the flattened round of dough into a lightly greased 9-inch round pie pan and patch any holes or tears that may have formed in that transition. Place the pan in the refrigerator while you assemble the filling.

Peel, core, and chop the apple into bite-sized pieces before tossing it into a large bowl with the lemon juice. Peel and dice the sweet potato in a similar manner before mixing it in as well. Add all the remaining ingredients for the filling, except for the butter, and stir gently to coat the fruit evenly with the dry ingredients. Remove the pie pan from the refrigerator and pour the fruit and nut mixture into your prepared crust. Cut the butter into very small pieces, and scatter the chunks atop your filling. Set aside.

Take your second disk of dough and roll it out in a similar fashion, but this time cut out shapes of your choice with a cookie cutter. Here’s your chance to get creative! I like arranging an artful pile of leaves around the edge, adding veins and other details with toothpick impressions, but there’s no right or wrong approach here.

Brush the exposed lip of the base crust with aquafaba, just a small patch at a time, before firmly but gently pressing the shapes in to adhere. Brush the exposed surface with additional aquafaba when everything is in place. Carefully slide the whole pie into your oven and bake for 10 minutes, and then lower the oven temperature to 350ºF (175ºC) without removing the pie. Bake for an additional 25 to 30 minutes, until the top crust pieces turn golden brown. Let cool before serving.