Melt the butter over medium heat, stirring as it foams. Keep going until it turns golden, smells nutty, and you see those toasty brown bits on the bottom. Pull it off the heat and let it cool 10–15 minutes. (if too hot it will melt the sugars)
Pour the warm butter into a mixing bowl and add both sugars. Beat for 2–3 minutes until the mixture looks glossy, thick, and slightly lighter.
Mix in the egg, the extra yolk, vanilla, and sourdough discard, should look smooth, rich, and shiny.
In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon.
Add the dry ingredients into the wet and mix just until the dough comes together — no dry streaks. Stop as soon as it’s combined (do NOT over mix)
Use a spatula to gently fold in your chocolate chips.
Chill the dough for at least 2 hours, but overnight is truly the sweet spot. The texture becomes thick, chewy, and perfect. The cookies also spread less. *Don’t skip this step — it changes everything.*
Preheat the oven to 350°F (175°C) and line a baking sheet with parchment.
Scoop dough (about 2 tablespoons ) shape into balls and bake 12 minutes.
The edges should look set, but the centers should still look glossy and soft. They’ll finish cooking on the hot pan, so resist the urge to bake longer.
Let them rest on the tray for 5 minutes, then move to a rack to cool.
