Special equipment: potato ricer or food mill
Place potatoes in a large pot of cold water to cover by 1-inch. Bring potatoes to a boil and cook until tender, about 30 minutes. Drain in a colander. Force potatoes, while still warm, through ricer into a large bowl. Add butter and stir with a wooden spoon, letting butter melt completely. Add 1 cup cream and incorporate by gently stirring with wooden spoon, adding more cream to thin to desired consistency.