In a food processor, pulse pistachios and salt until fine meal texture.
Add butter, coconut sugar, egg, and vanilla to pistachios. Cream together until light and fluffy.
Add flours and starch to butter mixture. Pulse until dough forms.
Add cacao nibs last and pulse till combined.
Remove dough from food processor and divide into two.
Roll dough into a 2 inch diameter wide log. Wrap in Saran Wrap and refrigerate an hour. Repeat with other half of dough.
Preheat oven to 350 degrees.
After refrigerating, remove dough from refrigerator and unwrap.
Combine sugar, pistachios, and cacao nibs on a plate.
Brush beaten egg around log.
Roll dough in pistachio mixture and slice into 1/4 inch discs.
Place on lined cookie sheet and bake in oven 10 minutes.
Remove from oven, transfer cookies to wire rack, and cool completely before consuming :)
Enjoy!