Put the potatoes in a sauce pan and add enough cold water to cover them by 3 inches. Bring to a boil over high heat and cook, uncovered, for 15 to 20 minutes, until fork tender. Drain the potatoes and set aside. In a saucepan, combine the cream and butter and heat over medium heat to melt the butter. Raise the heat and bring the cream to a boil. Add the potatoes, mashing them with a fork as they are mixed with the cream. Do not mash them too much; they should be a little lumpy. Season with salt and serve hot.