Cut raw potatoes into roughly equally sized pieces.
Bring ~12 cups of water to a boil; add cut raw potatoes; boil ~15 minutes, until a potato piece breaks apart when poked with a fork.
Drain potatoes, return to hot kettle; add butter; use a potato masher OR a mixer until butter is mixed in and potatoes are lumpy but mashed.
Add milk, sour cream, garlic, salt, and pepper; mix vigorously until well combined and a bit “fluffy”.