To a bowl sift together flour, cream of tartar, baking soda, baking powder and salt. Set aside.
To a separate bowl mix your cinnamon and sugar coating together. Set aside.
Using a hand or stand mixer cream together softened butter, brown sugar and sugar until fluffy, about 2 minutes.
Add maple syrup, vanilla and milk to the butter and sugar and continue mixing until incorporated.
Slowly add the dry ingredients to the wet. Mix until the dough comes together. Scrape the bowl down and mix one more time. The batter will be extremely soft.
Use an ice cream scoop that has the lever that cleans out the scoop to create the cookies.
Roll each cookie dough ball into the cinnamon and sugar until fully coated. The dough balls will be soft and won't keep their shape. Just gently roll them around and place in a parchment lined container. Chill the formed cookie dough balls for 1 hour.
Preheat oven to 350 degrees.
Bake 5 cookies at a time on a parchment lined sheet pan for 13 minutes in the middle rack.
Right when done baking, remove the pan from the oven and bang once on the counter. If a significant mound remains in the center of the cookies, place back in the oven for 2-3 more minutes. This will be necessary for the cookies that chilled longer than 1 hour.
Leave cookies to cool on the sheet pan for 2 hours. If you don't have enough sheet pans, let the cookies rest for at least 15 minutes on the sheet pan, slide the parchment paper off with the cookies, rinse the pan off to remove any residual heat then line with new parchment paper and bake another batch. You don't want a hot pan to start with or the cookies will spread too much.
The cookies set overnight beautifully and create the best texture and flavor if you can wait. These are a perfect make-ahead cookie that get better with time.