Preheat oven 350°F
Beat butter and granulated sugar with a stand mixer fitted with a paddle attachment on medium speed until creamy, about 2 minutes
Add eggs, 1 at a time, beating until just combined after each addition. Beat in vanilla
In a medium bowl, stir together flour, cocoa, baking powder, salt, and cinnamon. Gradually flour mixture to butter mixture, beating on low speed until just combined. Beat in chopped pecans until combined. This will be thick.
Lightly dust hand with powdered sugar to prevent dough from sticking. Divide dough in half. Shape each dough portion into a 12 x 3-inch long log. Arrange two logs 2 inches apart on a baking sheet lined with parchment paper.
Bake in preheated oven 25 minutes. Cool on baking sheet 30 minutes. Cut the log diagonally, 1/4 in thick slices using a bread or serrated knife. Use a sawing motion for a clean cut. Arrange the slices on its side back on the parchment lined baking sheet.
Return to oven and bake for 7 to 8 minutes. Turn slices over and bake until dry and crisp, about an additional 7 to 8 minutes. Transfer to wire racks and completely, about 20 minutes.
Store cookies in an airtight container up to 1 week