Place potatoes and garlic in a large pot and cover with cold salted water.
Bring to a boil and simmer 15–20 minutes until fork tender.
Drain potatoes completely and return them to the pot.
Mash potatoes and garlic using a potato masher.
Add butter, milk, salt, and black pepper while mashing until smooth.
Fold in sour cream if desired for extra creaminess.
Transfer to a bowl, top with butter and chives, and serve warm.
