Trim the top quarter-inch off the garlic head, then wrap it in foil and drizzle with olive oil. Seal the foil tightly and roast in a 375°F oven for about 60 minutes until soft and golden. Once cooled, squeeze the garlic cloves out of their skins. Place the quartered potatoes in a large pot and cover with cold water. Stir in 1 teaspoon kosher salt and bring to a boil over high heat. Reduce heat and simmer the potatoes until they become tender when pierced with a fork, about 15 minutes. Drain the potatoes and return them to the pot. Add the roasted garlic cloves. Warm the half and half with the butter until the butter melts completely, then pour into the pot. Season with salt and freshly ground pepper. Mash everything together until the potatoes reach a creamy texture with some small lumps remaining. Serve the mashed potatoes garnished with fresh herbs and an extra pat of butter if desired.