In the bowl of a stand mixer, beat the butter on medium speed until creamy, about 1 minute. Scrape down the bowl. Add the brown and granulated sugars and beat on medium speed until light and fluffy, 2 to 3 minutes, stopping once to scrape the sides of the bowl.
Then add egg, vanilla, and sourdough discard. Mix on low speed until mostly combined.
Grab a bowl and add the flour, baking soda, cinnamon, and salt. Stir, then add to the bowl that's on the stand mixer. Mix on medium speed until mostly combined, a few flour streaks are okay. Add the oats and chopped chocolate and mix on low speed until just combined. Remove bowl and use spatula to clean the sides and bottom of the bowl to make sure everything is incorporated.
Refrigerate dough for 1 hour (up to overnight - the longer you refrigerate, the more flavor they will have).
Preheat oven to 375 degrees F.
Line a baking sheet with parchment paper. Scoop dough into 55 gram balls and place 8 of them onto baking sheet.
Bake for 13ish minutes, until edges are just golden and center looks melty and slightly underbaked. (They will continue to bake when you take them out of the oven.) Remove from oven and place pan on wire rack. Sprinkle with a little flaky salt, if desired. Let cool for 5 minutes, then take cookies off the pan.