– 5 pounds Yukon Gold Potatoes  – Cold water to cover potatoes – 1/2 tsp salt – 1 stick salted butter softened – 1/2 cup sour cream – 1/2 cup whole milk  – 1/2 tsp garlic powder – 1/2 tsp ground white pepper – 1 1/2 tsp salt – 4 tbsp salted butter for garnish – Chives finely chopped