Mix Dry Ingredients: In a bowl, combine flour, cream of tartar, baking soda, and salt. Set aside.

Cream Butter & Shortening: In a mixing bowl, cream together butter and shortening until creamy.

Add Sugar: Gradually add 1 1/2 cups of sugar to the mixture, beating for about 2 minutes until fluffy.

Add Wet Ingredients: Beat in the eggs, one at a time, and then add vanilla extract.

Incorporate Dry Ingredients: Gradually add the dry mixture to the wet ingredients, blending until just combined (don’t overmix!).

Chill the Dough: Cover the dough with plastic wrap and refrigerate for at least 8 hours or overnight for best results.

Preheat Oven & Shape Dough: Preheat your oven to 350°F (175°C). Butter or line your cookie sheets with parchment paper. Divide the dough into four equal portions and roll each into a log. Slice each log into 12 pieces, then shape each piece into a small ball.

Cinnamon Sugar Roll: In a small bowl, mix the remaining sugar and cinnamon. Roll each dough ball into the cinnamon-sugar mixture.

Bake: Place the balls on the cookie sheet, spaced 3 inches apart. Bake for 10-12 minutes until slightly browned. Let cool for 5 minutes before transferring to a wire rack.