Peel the potatoes and cut them into evenly sized chunks.
Place the potatoes in a large pot, cover with cold water by about 1 inch, and add the salt.
Bring the water to a boil, reduce to a gentle simmer, and cook for 15 to 20 minutes until fork-tender.
Drain thoroughly and return the potatoes to the warm pot over low heat for 1 to 2 minutes to release excess moisture.
Warm the milk, butter, and minced garlic in a small saucepan over low heat for 3 to 5 minutes. Do not boil.
Mash the hot potatoes until most large lumps disappear.
Add about three-quarters of the warm milk mixture and fold gently.
Add more of the mixture gradually until the potatoes reach your preferred consistency.
Fold in the sour cream and black pepper.
Taste and adjust the seasoning. Garnish with chopped chives if desired, then serve hot.