Using a big spoon or spatula, combine softened butter and sugars in a bowl.
Add egg, stirring to combine.
Add sourdough discard and vanilla, stirring to combine.
Add flour, salt, and baking soda, mixing until just combined. Do not overmix.
Add chocolate chips and mix, again avoiding over-mixing.
Let sit in the refrigerator 15 minutes, then remove from fridge and let dough return to room temperature. Preheat oven to 350℉.
Using a baking sheet lined with parchment paper, drop on scoops of dough about 2-3 Tbsp in size.
Bake 6-8 minutes for a slightly chewier cookie, or 8-10 minutes for a cakier cookie.
Remove from oven and transfer to a cooling rack. Sprinkle some flaky sea salt on the cookies while still hot.