Preheat oven to 400º.
Mix together ½ cup sugar, cinnamon, chipotle powder; set aside. Sift together flour, cocoa, cream of tartar, baking soda, and salt. Stir chocolate chips into the flour mixture.
With a mixer, cream the butter and 3 cups sugar until light and fluffy. Add eggs one at a time to butter mixture, then add the dry ingredients a little at a time until incorporated. Be careful not to over-mix.
Roll heaping tablespoons of dough into balls and roll balls in sugar and spice mixture. Place on parchment-lined baking sheets, several inches apart.
Bake about 7 minutes, rotate cookie sheets, then bake 5 more minutes, until cookies are set in the center and beginning to crack. Let cookies cool on baking sheets for at least 10 minutes, then transfer to a rack to cool completely.
