01 - Place potatoes in a large pot and cover with cold, salted water.
02 - Bring to a boil over high heat, then reduce to a simmer. Cook for 15–20 minutes until the potatoes are very tender when pierced with a fork.
03 - Drain the potatoes well and return them to the hot pot. Let them sit for 1–2 minutes to evaporate excess moisture.
04 - Add butter and mash the potatoes using a potato masher or hand mixer.
05 - Gradually add in milk and sour cream, continuing to mash until smooth and creamy.
06 - Season with salt and pepper to taste. Add more milk if a thinner consistency is desired.
07 - Serve warm with additional butter, if desired.