- Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. 
- In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside. 
- In a large bowl, beat the softened butter and granulated sugar together until light and fluffy, about 2-3 minutes. 
- Add the egg and vanilla extract to the butter mixture, and mix until well combined. 
- Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix. 
- Scoop out tablespoon-sized portions of dough and roll them into balls. 
- Roll each ball in powdered sugar until fully coated, then place them on the prepared baking sheets about 2 inches apart. 
- Bake for 10-12 minutes, or until the edges are set but the centers are still soft. 
- Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.