Preheat your oven to 350 degrees, and line a large baking sheet with parchment paper or a non-stick baking sheet. Set aside. 

In a small bowl, stir together the flour, oats, salt, and baking soda. Set aside. In a medium bowl, beat together the butter, brown sugar, and white sugar until combined. Add in the egg yolk and vanilla extract and beat until combined. Add in the dry ingredients, and beat until there are no dry pockets of flour. 

Stir in the chopped chocolate until well incorporated. Scoop the cookies into large, two-tablespoon-sized balls and space evenly on your baking sheet. You should have 5 cookies- if you have way more, they are not big enough! Press the cookies down slightly, and bake for 14-16 minutes, or until the cookies are a light golden brown on the edges. Cool for 10 minutes on the baking sheet before eating!