Grease and line a 20 cm baking tin with baking paper.
Chop the Mars bars into smaller pieces, then add them to saucepan along with the butter and the golden syrup.
Place the pan over a low heat and stir until it has all melted together.
Place the rice krispies into a large mixing bowl, then pour the melted chocolate mixture over. Mix well until the rice krispies are completely coated.
Tip the mixture into the lined baking tin and press it down firmly. Set it aside whilst you get the caramel ready.
For the caramel, melt the butter and the soft brown sugar over a medium heat until it has melted. Pour the condensed milk in and mix well.
Bring it to the boil, then turn the heat down slightly, but so it is still bubbling. Stir it continuously for 2-3 minutes until it is dark and golden.
Pour the caramel over the rice krispies. Leave it to cool slightly before placing it into the fridge for about an hour to cool completely.
Melt the milk chocolate in a heat proof bowl over a pan of simmering water. Once fully melted pour it over the caramel and spread evenly into the edges.
Place it into the fridge for a couple of hours until the chocolate has set.
Once set, cut it into portions and serve.