I just found this recipe after watching nearly all of the episodes.
4 tablespoons unsalted butter, cut into 4 pieces
Combine butter, 2 tablespoons cream, 1/2 teaspoon salt, 1/4 teaspoon pepper, sugar, and sweet potatoes in large saucepan. Cooked, covered, over low heat until potatoes are fall-apart tender, 35-40 minutes.
Off heat, add remaining tablespoon cream and mash sweet potatoes with potato masher. Serve