Preheat the oven to 350 F. In a large bowl, mix together butter, peanut butter, and sugar until smooth. Add in the vanilla extract and flour, and mix until it is fully combined.
Fold in the Reese's pieces and chocolate chips. Roll the cookie dough into balls and flatten each one slightly. Place the cookies onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.