Instructions

 Adjust oven rack to middle position and heat oven to 375 degrees. Line 18 by 13-inch rimmed baking sheet with parchment paper or silicone baking mat. Whisk flour and baking soda together in medium bowl; set aside.
 Melt 5 tablespoons butter in skillet over medium-high heat. Continue to cook, swirling skillet constantly, until butter is dark golden brown and has nutty aroma, 1 to 3 minutes longer. Transfer browned butter to large heatproof bowl. Add remaining 2 tablespoons butter and stir until completely melted.
 Add brown sugar, granulated sugar, vanilla, water, and salt to butter; whisk until fully incorporated. Add egg yolk; whisk until mixture is smooth with no sugar lumps remaining, about 30 seconds. Let mixture stand for 3 minutes, then whisk for 30 seconds. Repeat process of resting and whisking 2 more times (mixture should be thick, smooth, and shiny). Using rubber spatula, stir in flour mixture until just combined (dough will be stiff), about 1 minute. Stir in chocolate chips and nuts, if using. Give dough final stir by hand to ensure no flour pockets remain and ingredients are evenly distributed.
 Working with 3 tablespoons dough at a time, roll into balls and space them 2 inches apart on prepared sheet. Bake until cookies are golden brown and still puffy and edges have begun to set but centers are soft, 10 to 14 minutes, rotating sheet halfway through baking. Let cookies cool on sheet for 5 minutes, then transfer to wire rack. Let cookies cool completely before serving. (Cookies can be stored in zipper-lock bag for up to 3 days.)