Break the candy bars into bits and drop them into a saucepan. Add the butter and melt, over lowish heat, stirring frequently with a rubber spatula. When everything is melted (the nougat-like layer takes the longest to go), tip in the cereal and turn them, with your rubber spatula, in the chocolate mixture until they are all pretty well coated.
Fill the mini muffin papers with the mixture and put in the refrigerator, on a small sheet pan or tray, for at least 1 hour.
Recipe courtesy of Nigella Lawson(Copyright 2004, Feast, Hyperion, All Rights Reserved)