Preheat oven to 350°. Line a 9x13 light colored cake pan with foil and spray with non stick cooking spray. Set pan aside.
In a medium sized bowl, whisk together flour, baking soda, and salt and set aside.
In the bowl of a stand mixer, or in a large bowl with a hand mixer, beat butter and sugars together until fluffy. Add eggs one at a time and continue to mix until well combined. Add vanilla extract.
With mixer on low speed, slowly add flour mixture to bowl and mix until combined, scraping sides of bowl as needed. Stir in chocolate chips and Reese's Pieces.
In a small saucepan, warm peanut butter over medium low heat just until it reaches a pourable consistency.
Transfer 1/2 of cookie dough to lined cake pan and spread into an even layer. Pour peanut butter over first layer of cookie dough and spread evenly. Take spoonfuls of remaining cookie dough and drop all over peanut butter layer. Use an offset spatula to carefully spread top layer of cookie dough into an even layer.
Sprinkle with additional mini semi sweet chocolate chips and Reese's Pieces. Bake for about 30-35 minutes, until cookies bars are light golden brown. Do not over bake. Cookie bars will continue cooking and set as they cool.