Cover the potatoes with 1 inch of cold water in a large saucepan. Bring to a boil, then reduce to a simmer and cook until the potatoes are fork tender, about 20 minutes. In a small pot over low heat combine half-and-half and butter. Heat until hot but not simmering.
Drain the potatoes in a colander, tossing to remove any excess water. Wipe the saucepan dry. Add the potatoes back to the saucepan and mash to a uniform consistency (or process through a food mill back into the dry pot). Give it a quick mix with a hand mixer to incorporate some air and ensure a smooth texture. Do not overmix or potatoes will become gummy.
Using a flexible rubber spatula, fold in the melted butter and half-and-half mixture until just incorporated. Fold in sour cream and 1/4 cup chives and season with salt and pepper.
Transfer to serving bowl and garnish with chopped chives.