Grease a swiss roll tin.
Put the butter, mars bars and golden syrup in large pot and melt slowly, keep mixing well untill it's all melted together.
Add the rice Krispies and mix well being carefull not to smash the krispies. Press into prepared tray.
Melt the cooking chocolate and spread over the top of the krispie mix.
Chill and cut into slices to serve.
Once your chocolate is spread over the top shake the tray to make it smooth out.