Some spuds just can't cut it as a jacket spud. They go all mushy and watery in the middle. I grow the variety called Nicola, which isn't at all good for mashing (glue...) but which makes great oven chips and jacket spuds. I just give 'em a scrub, prick them lightly a few times with the point of a knife (stops them exploding in the oven) then sprinkle them with salt while they're still a bit damp. No oil. Into a preheated oven at 200°C for about an hour, depending on size, straight on to the shelf. When they come out, I give each one a bash with my fist, not quite enough to bust the skin. Then it's a simple case of far too much butter.