In the bowl of stand mixer fitted with the paddle attachment (alternatively you can also use a mixing bowl with an electric mixer), beat butter, sugars, and vanilla on medium-high until super light and fluffy, about 3-5 minutes.
Scrape down the sides of the bowl with a spatula. With the mixer on low, carefully add the flour then the chocolate chunks. Beat just enough to blend.
Divide dough in half then place each half on a large piece of plastic wrap. Fold plastic over to cover dough and to prevent your hands from getting all sticky. Using your hands, form dough into a log shape. Each half should form logs that are 2–2 1/4" in diameter. Chill until firm, about 2 hours.
Preheat oven to 350 °F (177 °C). Line a rimmed baking sheet with a silicone baking mat or parchment paper.
Unroll the logs of dough then brush them with the egg on all sides. Sprinkle and coat the logs in sparkling sugar and gently pat them to get them to stick. It's okay if it's not totally coated.
Slice each log about 1/2"-thick rounds. Place on prepared baking sheet about 1-inch apart. Sprinkle with sea salt.
Bake for 12-15 minutes, or until the edges are just beginning to brown. Let cool on baking sheet for 5 minutes then transfer to a wire rack to cool completely.
Notes
Cookie dough can be made 1 week ahead. You can tightly wrap them in plastic wrap and chill, or freeze up to 1 month.Cookies can be baked 5 days ahead. Store in an airtight container.From Alison Roman's Dining InBon Appétit featured on .