Preheat oven to 350°F. Make the brownies according to the instructions on the package. Use a small cookie cutter or the top of the mason jar to cut circles of cooked brownies out of the 9×13 pan. Place the brownie circles in the mason jars.
Chocolate Layer:
Pipe chocolate frosting into each jar, over the brownies.
Peanut Butter Cup Layer:
Cut the peanut butter cups into chunks and place them on top of the chocolate frosting in the jars.
Peanut Butter Frosting:
Mix together the vanilla frosting and peanut butter. Add the powdered sugar and mix well. Beat in 3 tablespoon half-n-half until smooth and creamy. Pipe the peanut butter frosting over the peanut butter cups in the jars.
Top each frosting peak with 1/4 of a peanut butter cup and store in the fridge until ready to serve!