Combine butter, cream, salt, sugar, and sweet potatoes in 3 to 4 quart saucepan; cook, covered, over low heat, stirring occasionally, until potatoes fall apart when poked with fork, 35 to 45 minutes
2
Off heat, mash sweet potatoes in saucepan with potato masher, or transfer mixture to hopper of food mill and process into warmed serving bowl. Stir in pepper; serve immediately.