In a medium saucepan, cook the potatoes in salted water until tender, about 15 minutes. Drain the potatoes and return them to the saucepan.
Add the butter, sour cream and garlic. Mash the potatoes with a potato masher or the back of a fork until the ingredients are blended. Add the milk, 1 tablespoon at a time, until the potatoes are the desired consistency. Taste and add salt and pepper, if needed.