Step 1

Preheat oven to 400 degrees, with racks in upper and lower thirds. In a medium bowl, sift together flour, cocoa powder, cream of tartar, baking soda, and salt. In a large bowl, using an electric mixer, beat butter and 1 1/2 cups sugar on medium speed until light and fluffy, about 2 minutes. Scrape down side of bowl. Add eggs and beat to combine. With mixer on low, gradually add flour mixture and beat until combined.

Step 2

In a small bowl, combine remaining 1/4 cup sugar, cinnamon, and chile powder (if using). Using heaping tablespoons, form balls of dough and roll in cinnamon-sugar mixture. Place, about 3 inches apart, on two parchment-lined baking sheets. Bake until cookies are set in center and begin to crack, about 10 minutes, rotating sheets halfway through. Let cookies cool on sheets on wire racks 5 minutes, then transfer cookies to racks to cool completely. (Store in an airtight container, up to 1 week.)