Peel and dice potatoes. Add to a pot of cool water along with 1 teaspoon of salt. Heat over high heat until water comes to a boil. Reduce heat to medium to maintain a slow boil.
2 pounds Yukon Gold potatoes
When potatoes are fork tender, drain water. Let potatoes sit for 1-2 minutes in pot so any excess water can evaporate. The heat from the potatoes will help the excess water evaporate.
Mash potatoes with a potato masher.
Place milk and butter in a microwave-proof dish. Heat just until warm.
3 tablespoons butter, ⅓ cup milk
Add half of the warm milk and butter to the potatoes. Stir well.
Add sour cream and the rest of the warmed milk. Stir in salt and pepper.
⅓ cup sour cream, ¼ teaspoon salt, ⅛ teaspoon pepper