Heat the oven to 400°F (200°C). Slice the top from the garlic head, drizzle with olive oil, wrap in foil, and roast 35 to 40 minutes, until soft. Squeeze the roasted cloves from the skins.
Place the potatoes in a pot, cover with cold salted water, bring to a boil, and simmer 15 to 20 minutes, until very tender.
Drain the potatoes well and return them to the hot pot for 1 minute to dry slightly. Warm the cream and butter together, then mash them into the potatoes with the roasted garlic.
Stir in the Parmesan, cream cheese, salt, and black pepper. Fold in the parsley or chives and serve hot.