Preheat oven to 400°F. Break the heads of garlic apart. Peel each clove and slice them in half lengthwise.
Place the halved cloves on a sheet of foil and drizzle with 1-2 teaspoons of olive oil. Fold the foil into a a pouch and place it seam-side up on a baking sheet. Roast for 10 minutes until the garlic is soft and yellow in color.
Dice the potatoes and place them in a 3.5-quart pan. Add 2 tablespoons of kosher salt and fill the pan with enough water to cover the potatoes. Boil for 15-20 minutes or until you can easily pierce the potatoes with a fork.
Once the potatoes are soft enough, drain and return them to the pan. Add the roasted garlic cloves, butter and pepper and toss the potatoes in butter until it melts.
Mash the potatoes using a potato masher. Gradually add the heavy cream as you mash. Once you're happy with the texture, taste the potatoes and add salt and pepper if desired.
Finish the potatoes off by giving them a final stroke using a metal whisk. Transfer them to a serving dish and top with a pat of butter and fresh pepper. Garnish with sliced green onions (optional).