1Heat oven to 350°F. In large bowl, beat butter, peanut butter and brown sugar with electric mixer on medium speed 2 minutes or until creamy. Beat in egg. On low speed, beat in banana and vanilla until smooth.
2In small bowl, mix flour, baking powder, baking soda and salt. On low speed, beat flour mixture into peanut butter mixture.
3Onto ungreased cookie sheet, drop dough by rounded tablespoonfuls about 1 inch apart.
4Bake 12 minutes or until golden brown. Cool 2 minutes; remove from cookie sheet to cooling rack. Drizzle cookies with melted frosting and sprinkle with peanuts.