Preheat your oven to 350 degrees F and line a quarter sheet pan with parchment paper or spray it with nonstick baking spray.  This recipe can also be made in a 9x13 cake pan but a quarter sheet pan is just the right height! 

Add the softened butter and brown sugar to the bowl of a stand mixer fitted with the paddle attachment. Beat on medium speed until well combined, about 1 minute. 

Next, add the eggs and vanilla extract and mix to combine. Make sure to scrape down the sides of the bowl as needed.

Next, add the oats, flour, and baking soda. Mix on low speed, just until combined.

Finally, add the chocolate chunks and fold them into the dough.

Transfer the dough to the prepared pan and spread it into a smooth, even layer. 

Bake for 28-30 minutes, or until the bars are golden brown around the edges and fully set in the center. 

Allow the cookie bars to cool completely in the pan. Then, remove them to a cutting board and slice them into your desired size.