
Cut the potatoes into large, even pieces (about 1½-inches). Place them in a pot with the garlic cloves and salt. Cover the potatoes with cold water by 1-inch.
Place the pot over high heat and bring the mixture to a boil. Reduce the heat to medium-low and simmer the potatoes for about 20 minutes, or until they are fork-tender (but not falling apart).
Meanwhile, heat a small saucepan with the milk and butter over medium heat, stirring occasionally, for about 5 minutes, until the milk is warm and the butter has melted. Remove from the heat and hold the mixture warm.
Drain the potatoes and garlic and return them to the large pot. Pour the milk mixture over the potatoes. Using a potato masher, mash the potato mixture just until smooth. (Don’t overmash or overmix, or the mixture will be gummy).
Stir in the sour cream and black pepper. Season the potatoes to taste with more salt and black pepper. Serve them warm topped with more butter.