Whisk together flour, baking soda, cream of tartar, and salt; set aside.
Cream butter and sugar until light and fluffy. Add eggs one at a time.
Add milk and vanilla and beat to combine.
Reduce mixer speed to low and slowly add dry ingredients until just incorporated.
Scoop with a medium cookie scoop or roll about 2T sized bits of dough into balls. Chill completely (about 30 minutes or wrap and chill overnight).
In a small bowl, whisk together the cinnamon and sugar. Roll the chilled dough in the cinnamon sugar and place on parchment-lined baking sheet.
Bake in preheated oven about 10 minutes or until puffed and set around the edges.
Cool and eat!
Notes
Yield: 36 cookies
In the video I made a half batch. You can also freeze the cookie dough and bake from frozen.
Store extra cinnamon sugar in a sealed container and add to oatmeal or save for more cookies!