Heat oven to 350.In medium bowl,beat brownie mix,melted butter,cream cheese and egg 50 strokes with spoon until well blended(dough will be sticky).
Drop dough by rounded tablespoons 2 inches apart onto ungreased cookie sheets to make 24 cookies;smooth edge of each to form round cookie.
In small bowl,mix powdered sugar and peanut butter with spoon until mixture forms a ball.With hands,roll rounded teaspoonfuls peanut butter mixture into 24 balls.Lightly press 1 ball into center of each ball of dough.
Bake for 10 to 14 minutes or until edges are set.Cool 1 minute;remove from cookie sheets.Cool at least 30 minutes.
Spread thin layer of frosting over peanut butter portion of each cooled cookie.