Peel the potatoes and cut them in 1-inch chunks. Place them in a large, deep saucepan, cover with water, and bring to a boil. Lower the heat and simmer for 20 to 25 minutes, until very tender. Drain and return the potatoes to the saucepan.
Meanwhile, heat the half-and-half and butter in a small saucepan over medium heat until the butter melts. Off the heat, add the truffle butter and allow it to melt. If the butter doesn't melt completely, heat the mixture slightly but don't allow the truffles to cook! With a hand mixer, beat the hot potatoes in the pot until they are broken up. Slowly beat in most of the hot truffle cream, the Parmesan, 2 1/2 teaspoons salt, and 1 teaspoon pepper and beat until the potatoes are thick and smooth. (You may have some truffle cream left over - reserve it for reheating.)
To keep the potatoes hot or to reheat them, place them in a heatproof bowl set over a pot of simmering water. Heat slowly, adding more truffle cream if the potatoes get too thick. Season to taste and serve hot.