Bring a large pot of salted water to a boil over medium heat. Cook the potatoes until tender, about 25 minutes. Drain well.
Combine the milk and garlic in a medium saucepan and simmer for 5 minutes.
In a large serving bowl, add the potatoes and mash them while slowly adding the milk mixture, butter, salt, and pepper, to taste, to the desired consistency. Taste and adjust the seasoning, if necessary.