Grease a 20cm x 30cm (8-inch x 12-inch) rectangular pan, line base and long sides with baking paper, extending paper 5cm (2 inches) over sides.

Stir butter, sugar, syrup and peanut butter in a large saucepan over low heat until sugar dissolves. Bring to the boil. Reduce heat, simmer, uncovered, without stirring for 5 minutes.

Gently stir in corn flakes. Spread mixture into pan, press firmly. Refrigerate about 30 minutes or until set.

Melt chocolate in a small bowl over a small saucepan of simmering water (don't let water touch base of bowl) until smooth. Spread chocolate over slice, stand at room temperature until set, before cutting.