Place butter and sugars into the bowl of a stand or electric mixer. Beat until creamy and light. Add eggs and vanilla beating until well combined.
Place flour, baking soda and salt into a large bowl, mixing to combine then slowly add to wet ingredients. Add chocolate chunks and mix until just combined.
Transfer half of dough into prepared baking pan, pressing evenly. Place unwrapped peppermint patties over first half of cookie dough. Place remaining half of cookie dough over peppermint patties, pressing to flatten dough.
Bake for 38-45 minutes or until baked through. Be sure to Let the cookie bars cool completely before cutting into squares. Takes about an hour. Be patient, it is finishing setting up!!
Cut cooled bars into squares and serve.
If you would like a thinner bar, use the same recipe plus one more bag of Peppermint Patties and arrange in a 9x13 inch baking dish. Watch baking time after 25-30 minutes in the larger pan. Enjoy!