Prepare the baking sheet: Line a baking sheet with parchment paper and set it aside.

Mix the dry ingredients: In a large bowl, whisk together the flour, baking soda, cream of tartar, and salt. Set aside.

Cream the margarine and sugar: In the bowl of a stand mixer, beat the margarine for about 1 minute until smooth. Add the sugar and beat until well combined.

Add the wet ingredients: Add the eggs, milk, and vanilla extract. Beat until fully incorporated, scraping down the sides of the bowl as needed.

Combine wet and dry ingredients: Add the dry ingredients to the mixer in two additions, mixing just until combined. Be careful not to overmix.

Preheat the oven: Preheat the oven to 375 degrees.

Prepare the cinnamon sugar coating: In a small bowl, mix together the sugar and cinnamon for the coating.

Shape and coat the dough: Scoop the dough and form it into 2 inch balls. Roll each dough ball in the cinnamon sugar mixture until fully coated.

Flatten slightly: Place the dough balls on the prepared baking sheet about 2 inches apart. Use the bottom of a drinking glass or measuring cup to gently flatten each one slightly.

Bake: Bake for 12 to 13 minutes, just until the cookies are lightly golden.

Cool: Let the cookies rest on the baking sheet for 1 minute, then transfer them to a cooling rack to cool completely.

Store: Store cooled cookies in an airtight container or storage bag.