Preheat oven to 375 and line two baking sheets with parchment paper.
Combine flour, baking soda, and cream of tartar in a medium mixing bowl. Whisk to combine. Set aside.
Cream butter and sugar in the base of a stand mixer until light and fluffy. Add eggs, one at a time beating until incorporated.
Beat in milk and vanilla until well combined, being careful not to over mix.
Slowly add the flour mixture and mix until combined.
In a small bowl whisk together 1 ½ teaspoons cinnamon and 6 tablespoons granulated sugar. Form dough into balls that are approximately the size of ping pong or golf balls. Roll in the cinnamon sugar to generously coat. Place 1 inch apart on baking sheet and flatten slightly with a glass.
Bake 9 minutes and let cool completely on a wire rack. Do not overbake!!
Notes
Modified from Better Homes and Gardens Heritage Cook Book, 1975 Edition. Makes 3 dozen