I've adapted this excellent recipe from Cook’s Illustrated. Their trustworthy test kitchen recommends Ghirardelli chocolate chips, and so do I. Do use fresh dark brown sugar (don't substitute light brown) and unsalted butter; salted butter has more water in it and that affects the cookie texture. Remember a few baking basics, and you’re going to have boy-next-door-worthy cookies in no time. These cookies taste divine when reheated in the microwave for 10-15 seconds. The chocolate melts and gets all over your fingers. Chase with a glass of cold milk, and baby, that’s all she wrote.
Adjust oven rack to middle position and heat oven to 375 degrees. Line 2 18- by 12-inch heavy baking sheets with parchment paper. Whisk flour and baking soda in medium bowl; set aside.
Heat 10 tablespoons of the butter in skillet over medium-high heat until melted, about 2 minutes, swirling pan constantly until butter is dark golden brown and has nutty aroma, 1 to 3 minutes. Take care not to burn the butter (it can happen quickly). Transfer hot browned butter to large heatproof bowl. Stir remaining 4 tablespoons butter into hot butter until completely melted.
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 30 seconds. Repeat process of resting and whisking 2 more times for a total of four 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. Chill the dough for 20 minutes.
Divide dough into 16 portions, each about 3 tablespoons. Don’t be afraid of how big these are. Arrange 2 inches apart on prepared baking sheets, 8 dough balls per sheet. (Smaller baking sheets can be used, but will require 3 batches.)
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 to 14 minutes, rotating baking sheet halfway through baking. Transfer baking sheet to wire rack; cool cookies completely before serving.