Put the potatoes and garlic into a large saucepan. Add enough water to cover the potatoes. Bring to a boil. Cover and reduce heat. Simmer for 20-25 minutes or until potatoes are fork tender.
Drain and return the potatoes and garlic to the pot or transfer to a stand mixer.= bowl.
Using an electric mixer (or handheld potato masher), beat at medium speed for 1 minute or until smooth.
Add the milk, sour cream, butter, salt, and pepper. Add the chives, if using. Beat until well blended. Add additional butter, salt, or pepper if desired.