PREPARE cake batter and bake in 13x9-inch pan as directed on package; cool completely.
BEAT cream cheese and sugar in large bowl with mixer until blended. Add peanut butter; mix well. Blend in 1 cup Cool Whip; spread onto cake.
MELT chocolate as directed on package. Mix with remaining Cool Whip; spread over peanut butter layer. Refrigerate 1 hour.
serving size = 1 piece (73 g)