Preheat the oven to 350°F.

Prepare and roast the garlic: Trim about 1/4 inch off the top of the garlic bulb to expose the tops of the cloves. Place the bulb cut-side up on a piece of foil. Drizzle the exposed cut surface with some of the 1/3 cup extra-virgin olive oil from the ingredient list and sprinkle with a little of the 2 teaspoons sea salt (reserve the remaining oil and salt for the potatoes). Wrap the garlic bulb tightly in the foil and roast in the preheated oven for 40 to 60 minutes, until the cloves are deeply golden brown and very tender. Remove from the oven and let cool until you can handle it.

While the garlic roasts, cook the potatoes: Cut the peeled potatoes into even 1–2 inch chunks so they cook evenly. Place the potatoes in a large pot, add 1 teaspoon of the 2 teaspoons sea salt, and add cold water to cover the potatoes by about 1 inch. Bring to a boil, then reduce to a simmer and cook until the potatoes are fork-tender, about 15–25 minutes (depending on size).

Drain and reserve cooking liquid: Drain the cooked potatoes into a colander, reserving 1 cup of the potato cooking liquid. Return the potatoes to the pot or place them into a large bowl for mashing.

Make the roasted garlic paste: Unwrap the cooled roasted garlic, squeeze or scoop the softened cloves from their skins into a small bowl, and mash the cloves into a smooth paste with the back of a knife or a small masher.

Mash and finish the potatoes: Use a ricer or potato masher to mash the potatoes until smooth or to your desired texture. Fold in the roasted garlic paste, the remaining extra-virgin olive oil from the 1/3 cup in the ingredients, 1/2 cup of the reserved potato cooking liquid, and the remaining 1 teaspoon of the 2 teaspoons sea salt. Add freshly ground black pepper to taste. Continue folding until the mixture is creamy, adding up to the remaining 1/2 cup of reserved cooking liquid a little at a time if you prefer softer, creamier potatoes.

Serve: Transfer the mashed potatoes to a serving dish and serve hot. If desired, top with butter and sprinkle with chopped chives and/or rosemary and additional freshly ground black pepper.