Cost per Serving:
1. Preheat oven to 350°F. Butter bottom and sides of a 9-inch cake pan and line bottom with parchment. Butter parchment. In a medium bowl, whisk together flour, baking soda and salt.
2. In a large bowl, beat butter, both sugars and peanut butter with an electric mixer on medium-high speed until combined. Scrape down sides of bowl and beat in vanilla and eggs until smooth. Reduce mixer speed to low and add flour mixture, mixing just until a thick dough forms. Fold in chocolate chips, Reese's Pieces and peanut butter cups. Press dough into prepared pan.
3. Bake until brown on top but still soft in center, 40 to 45 minutes. Let cool in pan for 20 minutes. Run a sharp knife around edges of pan; transfer cake to a cooling rack. Let cool completely before cutting into wedges and serving.