1In 3-quart saucepan, mix potatoes and garlic; add enough water (salted if desired) to cover. Cover and heat to boiling; reduce heat. Simmer covered 20 to 25 minutes or until tender; drain. Shake pan with potatoes over low heat to dry. Mash potatoes and garlic in pan with potato masher or electric mixer until no lumps remain.
2In 1-quart saucepan, heat milk, whipping cream, butter, salt and pepper over medium-low heat, stirring occasionally, until butter is melted; reserve and refrigerate 1/4 cup mixture. Add remaining milk mixture in small amounts to potatoes, mashing after each addition, until potatoes are light and fluffy. (Amount of milk needed to make potatoes smooth and fluffy depends on kind of potatoes used.)
3Grease 2-quart casserole. Spoon potatoes into casserole; cover and refrigerate up to 24 hours.
4Heat oven to 350ºF. Pour reserved milk mixture over potatoes. Bake uncovered 40 to 45 minutes or until hot. Stir potatoes before serving.