Preheat the oven to 350 degrees F.
Dice the potatoes and boil in a pot of water until fork tender, 25 to 30 minutes. Drain and return to the pan over low heat. Mash the potatoes for 5 minutes to allow a lot of the steam to escape.
Add the butter, cream cheese, half-and-half, cream, some salt, pepper and roasted garlic. Stir/mash to combine. Test and adjust the seasonings.
Spread the potatoes into a large buttered baking dish. Dot the top with butter. Bake until heated through, about 30 minutes.
Potatoes can be made 1 day ahead of time and baked the next day.