Combine potatoes, water and 1/2 teaspoon of the salt in a medium saucepan; bring to a boil over high heat. Reduce heat to medium-high and cook until tender, about 8 minutes. Drain potatoes in a colander and return them to pan.
Place saucepan back over medium heat, add cream, roasted garlic, the remaining 1 1/2 teaspoons salt and white pepper and mash vigorously with a potato masher until fairly smooth, about 4 minutes. Beat in butter before serving.
Yield: 2 1/2 cups