1.Grease 20cm x 30cm pan; line base and long sides with baking paper, extending paper 5cm over sides. In a large saucepan, stir butter, sugar, corn syrup and peanut butter over low heat until sugar dissolves. Bring to the boil. Reduce heat; simmer, uncovered, without stirring, 5 minutes. Gently stir in cornflakes. Spread mixture into pan; press firmly. Refrigerate about 30 minutes or until set. Spread melted chocolate over slice; stand at room temperature until set.