Grease an oblong 15x30cm baking tin and line with baking parchment.

In a small saucepan, gently melt the mars bars, golden syrup and butter. When the mixture is well combined, add the rice krispies and stir until coated

Press the mixture into the lined baking tin and leave to set.

Melt the white chocolate in a bowl over a pan of simmering water.

Pour the melted chocolate over the cake and leave to harden. Cut into 12 squares and store in an airtight container.