Preheat the oven to 200°C (400°F/Gas 6). Tear pieces of foil, each large enough to wrap a potato in, and put in a pile. Wash the potatoes well and scrub the skins. Hold each potato over a piece of foil, prick it here and there with a fork, and while still damp (so it sticks) scatter over a heaped teaspoon of the pepper salt. The amount you need will depend on the size of the potatoes.
Wrap up each potato in foil and put on a baking tray. Bake for about 50 minutes or until the potatoes surrender easily when pressed. Remove from the oven. Take a little extra pepper salt, and crush it a little finer to serve on the side. Serve the potatoes hot and still in the foil, for everyone to unwrap their own. They should be halved down the middle, pressed up from the bottom to fluff up, then topped with a blob of butter and a good trickle of buttermilk. Sprinkle the crushed pepper salt over the top.