Preheat oven to 350 degrees F and line 2 large baking sheets with unbleached parchment paper or silicone baking mats.
In a large bowl, add egg and sugar; whisk for 20 seconds. Add butter, vanilla, salt, baking soda and cream of tartar; whisk well until no lumps. Add almond flour and stir until combined.
In a small bowl, combine sugar and cinnamon for coating.
Using small cookie scoop, roll 1 inch balls and roll in cinnamon sugar mixture. Place on baking sheet and gently flatten with your fingers until sides "crack" a bit. Repeat with remaining dough. Sprinkle more coating on top of cookies.
Bake for 10 minutes, remove from the oven and let cool for 15 minutes before enjoying.
Notes
Store: In a cookie jar for up to 5 days. You can add a slice of bread to help absorb moisture from air. If you find your cookies start to dry out, place them in an airtight container. I would not recommend doing so at the start because you don't want cookies to get soggy and floppy.
Freeze: In an airtight container for up to 3 months. Thaw on the counter for a few hours.
Cream of tartar substitute: It makes cookies tangy and chewy and differentiates them from regular sugar cookies. You can try using lemon juice or vinegar instead. I personally have not tested.
Do not overbake cookies: It is important to remove cookies while they appear underbaked and pale.
Coconut oil: I have not tried using it to make snickerdoodles but in my experience, it results in more crunchy cookies.
Any other flour: Gluten free flours are very finicky, all flours are. I recommend using only almond flour, not even almond meal, for proper snickerdoodle.