In a small bowl, stir peanut butter and confectioners' sugar until smooth. Chill 15 minutes. Meanwhile, in a large bowl, beat sugars, butter and cream cheese until light and fluffy. Add vanilla and egg. Combine flour, cocoa and baking powder; add to the cream cheese mixture and mix well. Roll into 1-in. balls. Place half of the balls 2 in. apart on a greased baking sheet. Make a depression in the center of each ball with your thumb; fill with 1 teaspoon of the chilled peanut butter mixture. Flatten remaining balls and place on top, pressing edges to seal. Bake at 350° for 8-10 minutes. Remove to a wire rack to cool. Combine frosting ingredients in s small bowl; stir until smooth. Frost cooled cookies.
