Peel potatoes, then cut into ½" cubes. Place potatoes in a large pot, then cover with luke warm water. Bring to a rapid boil then cook until potatoes are very tender. A knife should easily pierce through the potatoes with no resistance.
While the potatoes cook, add heavy cream (or whole milk), butter, and smashed garlic cloves to a sauce pan. Bring to a simmer and heat for 10 minutes. Discard garlic cloves, then set aside until needed.
Drain potatoes, then immediately transfer to a ricer or foley mill fitted with the attachment with the tiniest holes. Place the foley mill over a large bowl, then begin to turn the handle to press the potatoes through. The potatoes will fall into the bowl below.
To the bowl of potatoes, add warmed heavy cream and melted butter, sour cream, chives, salt, and pepper. Stir to combine. Serve with additional chives on top. Enjoy immediately!