Preheat oven to 350F. Line baking sheets with parchment paper and set aside.

In a large mixing bowl, whisk together oats, flour, cocoa powder, baking soda, and salt.

In another bowl using a handheld or stand mixer, cream together butter and sugars until light and fluffy, about 2 minutes.

Beat in egg, egg yolk, and vanilla, mixing untii just combined.

Add in dry ingredients and mixing until just combined. Do not over mix. Fold in chocolate chunks.

Drop dough by rounded tablespoon onto the prepared baking sheet. Bake for 10 -12 minutes.

Cool on the baking sheets for 2 minutes, then remove to a rack to cool 5 minutes longer.