This was a must share recipe which turns a rainy summer day into a cast of sunshine!   I simply used a "boxed" chocolate cake mix - added this creamy, rich filling and tantalized my family's tastebuds like never before!  Follow the cake mix directions -Bake cupcakes as directed.  In another bowl mix 1/2 cup of creamy peanut butter, 3 tablespoons of unsalted butter - softened works best - 1 1/2 cup of confectioner's sugar (a/k/a powder sugar)  and 3 to 4 tablespoons of milk. Mix for a good minute until fluffy.  Spoon the peanut butter filling into a pastry bag fitted with a plain round tip.  Take your completely cooled cupcake and insert the tip into the top of each cupcake; squeeze as much filling as possible until you see the top of the cupcake bulge slightly!  Frost with chocolate frosting or even skim a bit of the peanut butter filling on top and sprinkle with crushed nuts or crushed oreo peanut butter cookies - yes, they finally make peanut butter Oreos!!  Enjoy!