In a medium mixing bowl, whisk together the flour, baking soda, and salt. Set aside.
In a stand mixer using the paddle attachment, cream together the butter and both sugars. Add in the egg and beat on medium speed for 30 seconds. Turn the speed to low and add in half of the dry mixture. Once incorporated, slowly stream in the buttermilk followed by the rest of the dry ingredients. Using a rubber spatula, fold in the chocolate chunks. Cover the dough with plastic wrap and refrigerate for at least 2 hours. (I typically let it refrigerate overnight and bake my cookies the next day.)
When you’re ready to bake, preheat the oven to 350°F and line two cookie sheets with parchment paper.
Using a 3.25-ounce cookie scoop (I used a #10 scoop), scoop the dough so it overfills the scoop and then mound the dough to make a big ball, slightly smaller than a tennis ball. You should end up with 9 dough balls. Bake them, three per sheet tray on the middle rack of the oven, for 12 minutes. They’ll spread out quite a bit. If you like them a little less gooey, cook them for 3 minutes more. Let the cookies cool on the sheet tray while the second round bakes. Remove the first round of cookies to a cooling rack and reuse for the third and final round of baking.
Grant Melton is an Emmy Award-Winning Producer of the Rachael Ray Show, food writer and recipe developer. He's a contributor to Food52, NYT Cooking and Rachael Ray Every Day Magazine. He loves cookies, cocktails and kindness.