In a high-speed blender or food processor, blend almond flour, coconut flour, sweetener, salt, baking powder, and xanthan gum until combined. Add the apple cider vinegar and cubed butter, blending until well mixed. Fold in the egg.

Form the dough into a ball and divide it into two pieces, making one slightly larger than the other. Flatten each piece into a disk shape, wrap in plastic wrap, and freeze for 30 minutes.

Remove the larger disk from the freezer. Place it between two sheets of parchment paper on a flat surface. Roll out the dough to about 11 inches in width and length. Freeze the rolled dough for another 30 minutes.

Preheat your oven to 350F. Grease a 9-inch pie dish. Place the rolled dough into the dish, pressing it down and smoothing the sides. Cover the edges with tin foil and par-bake for 20 minutes.

While the crust bakes, prepare the filling. In a mixing bowl, combine the cherries, cranberries, lemon juice, sugar-free powdered sugar, cornstarch, and xanthan gum. Mix well and set aside.

Remove the second disk of dough from the freezer. Roll it out between two sheets of parchment paper to half an inch thickness. Cut even strips using a pizza cutter.

After 20 minutes, take the crust out of the oven, keeping the tin foil on the edges. Remove excess liquid from the cherry filling and pour it into the crust. Arrange the dough strips on top in a lattice pattern. Brush the crust with egg yolk and melted butter.

Bake the pie for 45-50 minutes, or until the top is golden. Remove from the oven and let it cool completely.