Break the milk chocolate into squares and place in a heatproof bowl with the butter. Set over a pan of simmering water and allow to melt. Remove from the heat and mix in the cream and golden syrup-by hand this takes a few minutes.
Break up the biscuits, mix with malteasers and marshmallows and fold into the chocolate mixture.
Spoon into lined cake tin
Chill for at least 2 hours or overnight is best
Decoration: Break the milk chocolate into square and place in a heatproof bowl over a pan of simmering water. Spread over the top and sides of the cake for an even finish.
Decoration: Break the white chocolate into squares, and melt in a heatproof bowl over a pan of simmering water. Drizzle all over the cake. Repeat with the dark chocolate. Leave at room temperature to set for at least 20mins before serving.