Preheat your oven to 350°F (175°C).
In a large mixing bowl, cream together the unsalted butter, packed light brown sugar, and granulated white sugar until light and fluffy, about 2-3 minutes.
Beat in the egg, egg yolk, and vanilla extract until fully incorporated.
In a separate bowl, whisk together the all-purpose flour, oats, baking powder, baking soda, and kosher salt. Gradually add this dry mixture to the wet ingredients, mixing until just combined.
Gently fold in the chocolate chips until evenly distributed throughout the dough.
Drop rounded balls of dough onto a baking sheet lined with parchment paper, spacing them about 2 inches apart. Bake for 10-12 minutes or until the edges are golden but the centers are still soft.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a cooling rack to cool completely.
