To begin, brown the butter. Cube the 2 sticks of butter and add it to a saucepan on the stove over medium heat. Mix with a wooden spoon or rubber spatula continuously as the butter melts and eventually starts to get foamy (about 5-7 minutes). Once the butter is brown underneath the foam, remove from heat and set aside to let it cool.
Allow the brown butter to cool completely before making the cookie dough. To speed up the process, I add ice to a glass or stainless steel mixing bowl and transfer the saucepan of browned butter to the bowl of ice to cool it down faster.
Preheat the oven to 350℉. Line a baking sheet with parchment paper and set aside. Once the browned butter has cooled completely, add it to a large mixing bowl. Add the brown sugar and granulated sugar. With an electric mixer, cream the sugars and brown butter together for about 2 minutes.
Next, mix in the egg and egg yolk one at a time. Add the vanilla extract. Finally, mix in the sourdough discard until just combined.
In a separate medium-sized bowl, sift together the flour, baking soda, and salt. Gradually add the dry ingredients to the bowl of wet ingredients, mixing until just combined. Use a rubber spatula to scrape the sides of the bowl to incorporate all the ingredients.
Finally, fold in the chocolate chips. Scoop the cookie dough in 2-tablespoon-sized balls. Place them 2 inches apart on the baking sheet and bake for 10-12 minutes.
The cookies will be done when the outside edges are golden brown and the middle of the cookies are still slightly underbaked. Let the cookies rest on the baking sheet for a few minutes before transferring to a wire rack to cool completely. Enjoy!