Preheat the oven to 400°F (200°C). Slice the top off a head of garlic so the cloves are partly exposed, drizzle with 1 tablespoon olive oil, wrap in foil, and roast for 30–35 minutes until soft and caramelized. Let cool.

Peel and halve the potatoes if large. Place in a large pot and cover with cold water by an inch. Add 1 teaspoon kosher salt and bring to a boil over high heat, then reduce to a simmer and cook until fork-tender, about 15–20 minutes depending on size.

While potatoes cook, heat the remaining 1 tablespoon olive oil and 2 tablespoons butter in a small skillet over medium heat. Mince 2 cloves of raw garlic and gently sauté for 30–45 seconds until fragrant but not browned; remove from heat.

When potatoes are tender, drain well and return to the warm pot. Allow steam to escape for 1–2 minutes—this dries them slightly and helps create fluffy mash.

Squeeze the roasted garlic cloves from their skins into a bowl and mash into a paste with a fork. Add the roasted garlic and the sautéed garlic to the potatoes.

In a small saucepan, gently heat the milk (and cream if using) with remaining butter until the butter melts and the liquid is warm. Do not boil.

Using a potato masher or ricer, mash the potatoes to your desired texture. For creamier potatoes, use a ricer. Gradually add the warm milk-and-butter mixture and sour cream, stirring until smooth and creamy. Season with salt, pepper, and a tiny pinch of nutmeg if using.

Taste and adjust seasoning. If the mash is too stiff, add a splash more warm milk; if too loose, simmer gently in the pot for a minute to firm up. Stir in chopped chives or parsley.

Transfer to a warmed serving bowl, top with a pat of butter and extra chopped herbs, and serve immediately while hot.