Preheat oven to 350°. Combine first 3 ingredients in large bowl; stir until moistened. Spread into a greased 9 x 13 baking pan. Cut 15 peanut butter cups into quarters and press on top of batter. Bake 20 minutes or until a toothpick inserted comes out clean. Cool 15 minutes. Meanwhile, combine cream cheese, butter, peanut butter anf vanilla in large bowl and beat with electric mixer until smooth and creamy. Add powdered sugar one cup at at time until well-combined and fluffy. Spread over top of cooled brownies. Sprinkle remaining quartered peanut butter cups over the top of frosting. Drizzle with melted chocolate. Refrigerate until set. Tip: If desired, make these bars the day before you need them.