Line an 9 inch square baking tin with baking paper, leaving some overhang so the slice can be easily lifted out once set.
Gently melt the milk chocolate in the microwave in short bursts, stirring between each burst until smooth. Add the Rice Krispies and fold until fully coated. Stir through the Maltesers, then press the mixture firmly into the prepared tin to form an even base. Chill in the fridge while you prepare the caramel.
In a microwave-safe bowl, combine the butter, condensed milk, golden syrup and caster sugar. Microwave in short bursts, stirring well between each one, until the mixture thickens into a smooth caramel.
Pour the caramel over the chilled Rice Krispie base and spread evenly. Top with Maltesers. Return the tin to the fridge and chill until the caramel is just set.
Melt the Maltesers spread with milk chocolate and stir until combined, then smooth it over the caramel layer.
Refrigerate for at least 2–3 hours, or until fully set. Once firm, lift out of the tin and slice into squares using a sharp knife.
