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.
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Notes
To use roasted garlic: Instead of boiling garlic cloves with the potatoes, you can roast a whole head of garlic and use that instead for a deeper flavor. Roasting garlic is really easy! Remove most of the papery skin from the garlic and trim off the head so you can see the cloves within. Drizzle some olive oil over so that the cloves are coated. Wrap the head of garlic in foil and roast at 400°F for about 40 minutes until soft and golden brown. Let it cool, then squeeze the roasted garlic out of the skin and add it to the pot with the potatoes when you're ready to start mashing.
Serving idea: Serve these potatoes topped with extra melted butter and finely chopped chives. Or take the toppings to another level with crumbled bacon or shredded cheese.
Cook the potatoes in an Instant Pot! Follow the method for cooking potatoes in my Instant Pot Mashed Potatoes recipes for an easy, hands-off way to boil potatoes.