Line a 18cm rectangle tin with greaseproof paper.
Break the kinder buenos into the little pieces. Chop up the wafers into chunks.
In a large saucepan melt the butter, kinder chocolate and golden syrup over a gentle heat stirring constantly until there are no or almost no more lumps of chocolate visible, then remove from the heat. Leave to cool.
Take the biscuits, mini marshmallows and some of the kinder bueno chunks and stir into the chocolate mixture until everything is completely covered.
Tip the mixture into the lined baking tin, and spread it out to the corners. Add extra kinder buenos to the top. Chill for at least 2 hrs then cut into 12 squares.