Sweet and white mashed potato swirl - a pretty dish for the holidays. ½ pounds white potatoes, diced in pieces, 1½ pound sweet potatoes, and diced pieces. 4 Tablespoons butter (divided) ½ + cup warmed milk (divided) Salt, Pepper. Is it me or does this dish scream gooey cheese, sour cream and chives. Basically cook potatoes, mix, add ingredients and enjoy hot.