Scrub potatoes with vegetable brush under cold running water. Peel and cut into 2-inch chunks. Place potatoes in large saucepan or pot. Add cold water to cover completely. Heat to boiling, then reduce heat to simmer. Cover and cook until tender, about 15 minutes. Drain well.
In large mixing bowl, rice, mash or mix potatoes with all remaining ingredients except citrus zest and truffle oil. Mash or beat until smooth. Mound in warmed serving bowl. Sprinkle with citrus zest and drizzle with white truffle oil, if used.