1. Preheat your oven to 400°F (200°C). Line two baking sheets with parchment paper.
2. In a large bowl, cream together the butter, shortening, and sugar until light and fluffy, about 2-3 minutes.
3. Add the eggs one at a time, beating well after each addition.
4. In a separate bowl, whisk together the flour, cream of tartar, baking soda, and salt.
5. Gradually add the dry ingredients to the creamed mixture, mixing until just combined.
6. In a small bowl, combine the 2 tablespoons of sugar with the cinnamon.
7. Shape the dough into 1-inch balls, then roll each ball in the cinnamon-sugar mixture until fully coated.
8. Place the balls 2 inches apart on the prepared baking sheets. Bake for 8-10 minutes, or until the edges are set but the centers are still soft.
9. Remove from the oven and let them cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.

Pro tip: If you’re like me and enjoy the aroma of cinnamon wafting through the house, you might want to double the batch. These cookies disappear fast!