1. Preheat the oven to 350°F and line two baking sheets with parchment paper.

2. In a large bowl, beat the butter, granulated sugar, and brown sugar until light and creamy.

3. Add the eggs and vanilla extract, then mix until fully combined.

4. In a separate bowl, whisk together the flour, cocoa powder, cream of tartar, baking soda, cinnamon, and salt.

5. Gradually add the dry ingredients to the wet ingredients and mix just until a soft dough forms.

6. Cover the dough and chill for 30 minutes so it is easier to handle and holds its shape while baking.

7. In a small bowl, stir together the rolling sugar and cinnamon.

8. Scoop the dough into 1 1/2 tablespoon portions and roll into balls.

9. Roll each dough ball in the cinnamon sugar mixture until fully coated.

10. Place the dough balls on the prepared baking sheets, spacing them about 2 inches apart.

11. Bake for 9 to 11 minutes, until the cookies are puffed and crackled on top with set edges.

12. Let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.