for 4 1/2 to 5 1/2 hours, or on HIGH for 2 1/2 to 3 hours, until the potatoes are very tender when pierced with a fork. Avoid lifting the lid during the first couple of hours so the heat and steam stay consistent.
Once the potatoes are tender, gently stir from the bottom with a broad spoon, turning the potatoes over so they are coated in the thickened evaporated milk and butter sauce. Taste the sauce and add a pinch more salt if needed.