Preheat oven to 350F, Line a large baking sheet with parchment paper, spray with pan spray. Set aside.

In a large bowl, combine the flours, protein powder, baking powder, xanthan gum, and salt. Set aside.

In a separate bowl, whisk together sugar substitute, eggs, and vanilla until well combined and smooth. Pour into the bowl with the dry mixture, stir to combine.

Add pistachios, mix well to combine.

Gently knead the dough to pull it together, then form dough into a loaf on the prepared pan.

Bake for 20-25 minutes, until golden brown on the outside. Remove from oven, turn heat down to 250F.

Use a very sharp knife - carefully - Cutting on a slight diagonal, slice each loaf into ½" slices.

Arrange slices on the pans. Bake for 15 minutes, flip each piece over and bake for another 15 minutes, or until desired texture.

Remove from oven, allow to fully cool.