Preheat the oven to 425°F and position a rack in the center.
Scrub the potatoes and pat dry. Prick each potato all over with a fork.
Rub potatoes with olive oil. Season generously with kosher salt and black pepper.
Set potatoes directly on the oven rack with a sheet pan underneath. Bake 65–75 minutes, turning once, until skins are crisp and centers are tender.
Split each potato lengthwise and fluff the flesh with a fork.
Dot with butter, add sour cream, and sprinkle with cheddar. Return to the oven 2–3 minutes to melt, if desired.
Finish with chives and serve hot.