Step 1

Preheat the oven to 400 degrees F and line several baking sheets with parchment paper. In a large bowl, whisk together the flour, cocoa powder, cream of tartar, baking soda, and salt. Set aside.

Step 2

In the bowl of an electric mixer, cream the butter and 1 1/2 cups sugar together on high speed, until light and fluffy. (about 3–5 minutes) Then beat in the eggs and scrape the bowl with a spatula. Turn mixer on low and slowly add the flour mixture into the butter mixture, until just combined. Do not overmix the dough.

Step 3

Mix the remaining 1/4 cup sugar and cinnamon together in a small bowl. Use a 1 1/2-tablespoon cookie scoop to measure out dough balls. Roll each ball in your hands to even them out, then roll in cinnamon sugar to thoroughly coat.

Step 4

Place the balls on prepared baking sheets, 2 1/2 inches apart. Bake for 8–9 minutes, until just barely golden around the edges. Cool for several minutes on the baking sheets before moving.