Preheat oven to 350 degrees and line 2 cookie sheets with parchment paper.
Using a large bowl, beat together the butter, brown sugar, and sugar until combined and creamy.
Beat in the eggs, 1 at a time until combined.
Beat in the vanilla.
Using another large bowl, whisk together the flour, cocoa powder, cream of tartar, baking soda, baking powder, and salt until combined.
Gradually mix in the dry ingredients into the wet ingredients until combined and a dough forms.
Using a small bowl, whisk together the 1 C of sugar and 1 tsp of cinnamon.
Using a small ice cream scooper, scoop out about 1 ½ tbsp of cookie dough.
Roll into a ball in your hands.
Coat cookie dough ball in the cinnamon-sugar mixture.
Place onto a cookie tray.
Place into the oven and bake for 10-12 minutes or until the edges are set and the middle looks soft.
Allow cooling completely before enjoying them.