Preheat oven to 350 degrees F. Line a 13x9" baking dish with foil, extending the sides of the foil over the edges of the pan. Spray the foil liberally with cooking spray and set aside.

In the bowl of a stand mixer, cream together the butter and brown sugar until smooth, about 2 minutes. Add in the peanut butter, eggs, and vanilla extract and beat to combine. Lastly, add in the flour, salt, oats, baking powder and baking soda until a soft dough forms.

Chop the Reese's PB Cups in half or quarters. Spread 1/2 of the dough into the prepared baking pan in an even layer; top evenly with the caramel sauce and top with the reserved PB cups. Crumble the remaining dough or "puzzle piece it" (flatten dough in your hands and gently kind of puzzle-it together) on top of the caramel and PB cups.

Bake for approx. 20-25 minutes or until the top is light golden brown and the center appears just about set. It's okay if it jiggles a little; it will set up as it cools and you don't want to over bake. Cool completely before lifting the bars out of the pan and cutting into bars.