Preheat oven to 425 degrees F.
Roast garlic: Slice off the top of the garlic head to expose the cloves. Place on a piece of aluminum foil. Then, drizzle with olive oil, and a generous pinch of salt and pepper. Wrap each garlic head tightly with the foil and place on a sheet pan. Roast at 425 degrees F for 40 to 45 minutes, or until the cloves are soft and caramelized.
Meanwhile, cook the potatoes: Bring a large pot of water to a boil, enough to fully submerge the potatoes. Then, add the cubed potatoes and bring back to a boil. Cook over medium heat for about 20 minutes, or until easily pierced with a fork. Drain.
Mash potatoes: In batches, press the cooked potatoes through a potato ricer. You can also use a regular potato masher. Note: I like to use a potato ricer to get a fluffy and lump-free texture.
Then, combine the mashed potatoes with warm heavy cream and melted butter, adding more cream as needed to achieve the right consistency.
Squeeze out the cloves from the roasted garlic, leaving some behind for garnish if desired. Mash the cloves with a little bit of the mashed potatoes (this helps it to incorporate better) and return it to the pot to incorporate with the rest of the mashed potatoes. Season with salt and pepper to taste.
To serve, garnish with roasted garlic cloves, chives, butter, and a few grinds of black pepper. Enjoy!