Line cold cast iron with 1/4"(!) cold butter on the bottom. Place cut potatoes( I usually cut 1/2" slices), season, cover and start on really low heat. As the temp comes up, the butter slowly heats up to the point that you are poaching your potatoes (they're almost submerged). As the temp rises the potatoes will start to crisp. At this point they are very soft; loosen them carefully if they are sticking. Usually, if you start gently moving, swirling the pan when the butter starts to brown and they start forming a crust, they won't stick. After 45 min to 1 hr. they should be very soft on the top, and with a golden crust underneath. Turn over, and the other side should brown in 15-20 min. Drain while hot, enjoy. AKA pommes fondantes(MPW), Maine/down East skillet potatoes (according to John Thorne in Serious Pig)