Start by placing the cinnamon chips in the freezer to get extra firm.
In a bowl, whisk together the flour, baking soda, cream of tartar, salt and set aside.
In the bowl of a stand mixer fitted with the paddle attachment (or with a handheld mixer) cream together the butter and sugars on medium speed for about two minutes until fluffy, then scrape down the sides.
Add the egg and vanilla and mix until combined, then scrape down the sides again.
On low speed, spoon in the dry ingredients until just combined and scrape down the sides once again..
Add 2 oz of the cold cinnamon chips to the batter and mix on low until just combined, then place the bowl of dough (covered with plastic wrap) in the fridge for 1 hour.
Preheat the oven to 350℉/177℃, and line two large cookie sheets with parchment paper.
In a small bowl, combine the 3 tablespoons of sugar and the cinnamon.
Remove the dough from the fridge. Using a 1.5-inch cookie scoop, roll the dough into balls (~45g each in between your hands, then cover completely in the cinnamon sugar mixture.
Add the dough balls to your prepared sheet pan. Only cook 6 cookies per pan, as they are rather large. To the top and sides of your dough balls, gently push in about 4-5 additional cinnamon chips (optional)
Bake for 11-13 minutes - they will look gooey and underdone - this is normal and what you want! Use a round item slightly larger than the cookie to gently move it around the cookie to make it nice and round.
Allow the snickerdoodles to cool for 1-2 minutes on the pan, then carefully transfer to a wire rack to cool.