Pre-heat the oven to 350 degrees. In the mixing bowl of a stand mixer, add the brownie mix, butter, cream cheese, and egg, and mix well. Batter will be a little gooey. Using a cookie scoop, scoop the batter out onto a parchment lined cookie sheet, making 24 cookies, and smoothing the batter to form round cookies. Bake the cookies for 12 minutes, or just until the cookies are done, and a little golden brown on the bottom. In a separate bowl, mix the powdered sugar and the peanut butter until its well combined. Form the mixture into 1 inch balls, making 24 balls, one for each cookie, and set aside. When cookies are done, remove from the oven, and press a peanut butter ball into the center of each cookie. The peanut butter balls will melt a little, but it's okay, just let them cool for about 10 minutes, and then transfer them to a wire rack to finish cooling completely.