Preheat the oven to 350 F. In a medium bowl, whisk together flour, cocoa powder, salt, and baking soda. In a large bowl, combine butter, brown sugar, and granulated sugar, mix until fluffy.
Add in egg and vanilla extract, and mix until smooth. Add in the flour mixture, and mix until a thick dough forms. Place the powdered sugar into a shallow dish.
Roll the cookie dough into balls, and fully coat in the powdered sugar. Place the cookies onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.
Remove the cookie from the oven, and top each one with a candy cane kiss.
