In a large saucepan, melt the butter and chocolate chips on low heat, stirring frequently. Remove from heat and add sugar, stir until well combined. Add eggs, one at a time, stirring until well combined. Add flour and salt and mix until combined.
Gently stir in chopped peanut butter cups. Pour evenly into prepared pan.
Bake for 25-30 minutes or until toothpick comes out with just a few "brownie crumbs" on it. Cool completely and frost with peanut butter frosting.
In a large mixing bowl, cream butter and peanut butter together until light and fluffy. Add powdered sugar, half-n-half and vanilla and beat until well combined.
Use the miniature peanut butter cups that come wrapped in foil, not the mini, mini ones that come already unwrapped in the bag.