1Heat oven to 350ºF. Grease 1 1/2-quart casserole. Place potatoes in 4-quart Dutch oven; add enough water (salted if desired) to cover. Cover and heat to boiling; reduce heat. Simmer about 10 minutes or until potatoes are tender; drain. Shake potatoes in Dutch oven over low heat to dry.
2In large bowl, mash potatoes until no lumps remain. Add milk in small amounts, beating after each addition (amount of milk needed to make potatoes smooth and fluffy depends on kind of potatoes used).
3Add sour cream, margarine, rosemary and salt. Beat vigorously until potatoes are light and fluffy. Stir in Havarti cheese. Spoon into casserole. Sprinkle with Cheddar cheese.
4Bake uncovered 30 to 35 minutes or until hot. Sprinkle with parsley.