Preheat your oven to 325 degrees F. Prepare a cooking sheet with nonstick cooking spray or parchment paper and set aside.
Cream together melted (and slightly cooled) butter with sugar and brown sugar in a stand mixer or in a large bowl with a hand mixer until well combined. Next beat in vanilla, cinnamon, egg, and egg yolk. Beat together for 2-3 minutes until smooth and creamy.
In a separate bowl shift together flour, salt, and baking soda. Slowly mix this with your wet ingredients until well combined. Last fold in oats and chocolate chips.
Roll out balls of dough and place them on your prepared baking sheet. Bake for 10-12 minutes. Allow to cool for 3-4 minutes on the baking sheet before moving it to a cooling rack.