Slice the top off the bulb of garlic, exposing the individual cloves. Drizzle with a little olive oil and wrap it in aluminum foil. Roast in the oven for about 30-35 minutes, until the cloves are soft and golden.
Meanwhile, bring a large pot of salted water to a boil. Add the cubed potatoes and cook until fork-tender, about 15-20 minutes.
Drain the potatoes and return them to the pot over low heat to evaporate excess moisture.
Squeeze the roasted garlic cloves from their skins into the potatoes. Add butter, heavy cream, and sour cream.
Mash the mixture until smooth and creamy. Adjust the texture with more cream if necessary.
Season with salt and pepper to taste, mixing well to incorporate.
Transfer to a serving bowl and garnish with chopped chives or parsley.
Notes
For a lighter option, substitute heavy cream with milk.