Direction :

1. Heat the oven to 350ºF.
2. Line a baking sheet with parchment paper.
3. Place the flour, cocoa powder, baking soda, and salt in a medium bowl and whisk to combine the ingredients. Set aside.
4. Put the butter and brown sugar in the bowl of a stand mixer. Fit the mixer with the paddle attachment and beat on medium speed for 2 to 3 minutes, stopping to scrape down the mixer once or twice, until the mixture is light and fluffy.
5. Turn off the mixer, add the egg and vanilla, and beat until the egg is thoroughly incorporated, 1 to 2 minutes.
6. Add the dry ingredients and mix on low speed until no flour is visible, stopping to scrape down the mixer once during the process.
7. Pour the granulated sugar into a small bowl. Portion out the dough using a 2-tablespoon scoop or measure or a scale — each portion should weigh 50 grams. You should have about 16 to 18 balls total. Roll each portion between your hands to form a ball; then roll in the sugar — coat each ball as generously as you are able to in the sugar. Transfer 6 balls to the prepared sheet. Bake for 12 minutes; remove from heat and allow cookies to cool completely on the sheet pan. Repeat this process, baking 6 cookies at a time.
8. Store the cookies in an airtight container at room temperature for up to 1 week or freeze for up to 3 months.