In the bowl of your stand mixer, cream together 1 cup unsalted butter, 1 cup brown sugar, and 1 cup granulated white sugar with the paddle attachment on medium speed until smooth.
Lower the mixer speed to low speed and add the 1 cup sourdough discard, 2 egg yolks, and 2 teaspoons vanilla extract. Mix until thoroughly combined, about 30 seconds.
Add the 2 ½ cup bread flour, 1 teaspoon kosher salt, and ½ teaspoon baking soda and mix on low speed until just combined.
Fold in 3 cups chocolate chips with a spatula.
Wrap the dough in wax paper and refrigerate for at least 2-3 hours.
Preheat the oven to 350°F (180°C). Remove the dough from the refrigerator and roll it into balls, about 2 tablespoons of dough each. Place the dough balls onto a baking sheet about two inches apart.
Bake for 16 to 18 minutes or until the edges are lightly browned but the center is still soft. Allow the cookies to cool for at least 5 minutes before transferring them to a wire rack to cool completely.
Notes
Use a kitchen scale to weigh your ingredients rather than the cup measurements.Use room temperature butter, eggs, and sourdough discard. Chilled eggs or sourdough discard may cause some of the butter to re-solidify prematurely. To quickly bring the eggs to room temperature, place them in a bowl of warm water for 10-15 minutes.Chill the dough for at least 2-3 hours before baking. Chilling allows the butter to firm up and the flour to absorb more liquid further solidifying the dough. If the dough is baked without chilling it first, the cookies will spread while baking and become thin, hard, and crispy. Use a cookie scoop for evenly portioned cookies. Take the guesswork out of portioning cookies by using a cookie scoop to make sure each cookie is the same size. Alternatively, you could cut the block of cookie dough into even pieces with a knife. I find that this method saves me time.Baking times for all recipes are only suggestions. The actual baking time will vary depending on your oven.Allow the cookies to cool for 5 minutes before transferring them to a wire rack.Storing: Baked cookies can be stored in an airtight container at room temperature for up to 4 days.