Preheat the oven to 400°F (200°C) and line a baking sheet with aluminum foil, leaving enough overhang to wrap the garlic in a packet.
Remove the papery outer layers from the garlic bulbs, leaving the bulbs intact. Cut off the top ½ inch of each bulb to expose the cloves.
Place the garlic heads, cut side up, on the prepared baking sheet. Drizzle with olive oil. Wrap the foil over the garlic to form a sealed packet.
Bake the garlic for 60–70 minutes, or until the cloves are soft and golden brown. Remove from the oven and let cool.
Place the potatoes in a large pot and cover with water. Bring to a boil over medium-high heat, then cook for about 25 minutes, or until the potatoes are fork-tender.
Drain the potatoes and return them to the pot, off the heat. Lightly mash them.
Add the butter and heavy whipping cream to the potatoes, then mash to your preferred consistency.
Squeeze the roasted garlic cloves into a medium bowl, discarding the skins. Reserve 3-4 cloves for topping and mash the rest of the garlic until smooth.
Add the mashed garlic, kosher salt, and black pepper to the potatoes. Mix until well combined.
Serve warm, garnished with melted butter, fresh parsley, and the reserved garlic.