Boil the baked potatoes with their peel in salted water for 40 minutes and leave to cool. Halve the potatoes lengthways and hollow out to a 1 cm thick edge. Mix the potato mixture with the herb butter, the parmesan and the chives and season with salt and pepper. Pour the mixture back into the potatoes, fold the potato halves together and wrap in aluminum foil. Heat the potatoes directly on the embers for 15-20 minutes.