6 to 8 large Yukon gold potatoes (about 3 1/2 pounds total), scrubbed
1 tablespoon plus 1 teaspoon kosher salt
4 garlic cloves (3 cloves lightly smashed for boiling water, 1 clove grated for butter)
1/2 pound (2 sticks) salted butter
1/2 cup milk, warm
1 teaspoon freshly ground black pepper
4 ounces cream cheese
1/2 cup sour cream
Peel the potatoes, leaving a little skin on each one for texture, if desired (I like to leave about 5 stripes of skin on each potato). Cut the potatoes into 1 1/2-inch chunks.
Add the potatoes and enough cold water to cover to a large pot and bring to a rolling boil. Add 1 tablespoon of the salt and the 3 smashed garlic cloves to the water and simmer potatoes until very soft, 15 to 20 minutes. Drain thoroughly, remove garlic, and return potatoes to the pot. Shake the potatoes in the pot to help any excess water evaporate.
Meanwhile, in a medium saucepan, heat the butter and grated garlic over medium-low heat just until the butter is melted and the garlic is fragrant. Remove from heat and add the warm milk.
Mash the potatoes using a potato masher, adding the milk mixture in about 4 parts, mashing as you go, until the potatoes are creamy and well blended but still have a bit of texture.
Add the cream cheese and sour cream.
Mash in the remaining 1 teaspoon salt and the pepper. Serve hot.
Store leftovers in a covered container in the refrigerator for up to 3 days.