Pierce the skin of each potato once or twice with the tines of a fork. If desired, pre-cook potatoes by baking them in a preheated 350 degree oven until just soft when pressed, about 1 hour.

Prepare a wood fire outdoors and let cook down to embers. Place each potato on a square of foil large enough to wrap it, dull side up. Sprinkle with olive oil, salt, and pepper, to taste. Rub oil and seasonings into potato, then gather foil around potato to cover it tightly. If using uncooked potatoes, place them in embers of the fire 1 hour before serving; turn every 15 minutes with long handled tongs (do not worry if foil starts to blacken). Roast until the tip of a knife slides into the potato easily (remove a potato from the fire and pull back foil to test; return to fire if not cooked through). If using pre-cooked potatoes, place them in the embers for 20 minutes to heat through, turning with tongs once or twice.

To serve, remove potatoes from fire with tongs. Unwrap potatoes with hot pads and cut open tops. Squeeze open potatoes to expose flesh and slather with plain butter or cilantro butter.