In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar using a handheld or stand mixer on medium-high speed until the mixture is fluffy and pale, about 2-3 minutes. Add the egg and vanilla extract, then beat on high until thoroughly mixed. Scrape down the sides of the bowl as needed.

In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients into the wet mixture while the mixer is on low speed. Continue beating until everything is well combined, then fold in the chocolate chips. The dough will be thick and sticky. Cover the dough tightly and refrigerate for at least 3 hours or up to 3 days to firm up.

After chilling, allow the dough to sit at room temperature for about 10 minutes. If chilled longer than 3 hours, extend the resting time to 20 minutes for easier handling.

Preheat the oven to 350°F (177°C). Prepare large baking sheets by lining them with parchment paper or silicone baking mats.

Roll the dough into 1.5-tablespoon-sized balls. First, lightly coat each dough ball in granulated sugar, then generously roll them in confectioners’ sugar. Arrange the dough balls 3 inches apart on the prepared baking sheets.

Bake for 11-12 minutes, or until the edges are firm and the centers remain soft. If the cookies are not spreading after 9 minutes, briefly remove the tray and gently tap it on the counter a few times to encourage spreading, then return to the oven to finish baking.

Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. They will deflate slightly as they cool.