1. COMBINE half the peanut butter with the dark chocolate until smooth. Combine the remaining peanut butter with the white chocolate until smooth. Cool slightly.
2. DROP spoonfuls of white chocolate mixture and dark chocolate mixture into a lined 12 x 22 cm loaf pan. Gently shake the pan to level mixture then pull a skewer backwards and forwards through the mixture for a marbled effect. Refrigerate until set. Cut into 18 squares.