These cookies are thin and chewy and perfect for making ice cream sandwiches or dunking into a glass of ice cold milk. Recipe adapted from Joy the Baker.
Preheat oven to 375°F. Cream butter and sugars together until pale and fluffy, about 5 minutes. Add eggs in one at a time, beating well after each addition. Mix in the vanilla, cream of tartar, baking soda, salt, cocoa powder, and cinnamon. Beat together one last time and make sure all the dough is a nice even brown. Mix in the flour just until the dough comes together. Over-mixing at this point makes for sad cookies. Scoop dough into tablespoon-sized mounds onto a parchment covered baking sheet. Bake about 9-10 minutes, just until the edges are set. Enjoy!