These cookies can be baked right away, but they are best after a nice cold blast in the fridge as it will minimize spread. After letting the dough rest in the fridge for at least 24 hours, preheat oven to 375 degrees F, and adjust rack to the middle position. Line 2 sheet pans with parchment or a silicone baking mat.

1. Whisk flour and baking soda together in medium bowl, and set aside.
2. Heat 10 tablespoons butter in a stainless steel skillet or small saucepan over medium-low heat until melted, about 2 minutes. Continue cooking, swirling pan constantly until butter is dark golden brown and has nutty aroma, 2 to 5 minutes. Turn off heat. Stir remaining 4 tablespoons butter into hot butter until completely melted; set aside.
3. Add both sugars, salt, and vanilla to bowl with butter and whisk until fully incorporated. Add egg and yolk and whisk until mixture is smooth with no sugar lumps remaining, about 30 seconds. Let mixture stand 3 minutes, then whisk for 60 seconds. Repeat process of resting and whisking 2 more times until mixture is thick, smooth, and shiny. Using rubber spatula or wooden spoon, stir in flour mixture until just combined, about 1 minute. Stir in chocolate chips and nuts (if using), giving dough final stir to ensure no flour pockets remain.
4. Using a large or 1/4 cup cookie scoop, divide dough into balls and arrange them side by side on a 9×13 baking sheet. Cover with plastic wrap and refrigerate for at least 24 hours. This cold rest time allows the flour to hydrate and the flavors to deepen. It’s the same reason we marinate meat — better flavor. Do you absolutely have to do this? No. But will they taste better? YES! In fact, you could let this dough rest in the fridge for up to 3 full days before baking.
5. When ready to bake, preheat oven to 375 degrees F, and arrange each dough ball 2 inches apart on prepared baking sheets, 6 dough balls per sheet. At this point, you can sprinkle each cookie with a pinch of fluer de sel sea salt — or you can do it immediately after they’re baked. You may have dough leftover, so bake a third pan after the first two are done.
6. Bake cookies 1 tray at a time until cookies are golden brown and still puffy, and edges have begun to set but centers are still soft, 10-12 minutes, rotating baking sheet halfway through baking. Transfer baking sheet to wire rack; cool cookies completely before serving.
7. Cookies can be stored in an airtight container or freezer bag for up to 5 days at room temperature. You can freeze them for longer storage, just make sure you wrap them individually with plastic wrap.