Preheat the oven to 350 degrees and grease a 13x9 inch baking pan with shortening
Place the brown sugar, butter, peanut butter, vanilla and eggs in a large mixing bowl. Beat with an electric mixer on medium speed until the ingredients are well incorporated.
Place the flour , baking soda, baking powder and salt into a medium size bowl. Stir to combine the ingredients. Add the flour mixture to the butter mixture, stirring the ingredients together until they are incorporated. Stir the cut up mini peanut butter cups and milk chocolate chips into the batter.Spread the batter evenly into your prepared 13x9 inch pan. Bake 25 - 30 minutes or until golden brown. Remove the pan from the oven to a cooling rack. Immediately place a whole mini peanut butter cup into the top of the brownies in what you would consider a serving. Starting at the short vertical end of the pan. I spaced out 4 mini peanut butter cups across the pan, then worked my way down the pan to make six rows. Cool brownies completely, cut and serve.