DH said that to cook JP in the oven from start to finish was a waste of energy and expensive so he suggested I parboil them for 10 mins with skins on in boiling water and then cook them in hot oven for 20 mins.
Perfect jacket potatoes!! Soft and moist in the middle and crispy on the outside.
Scrub potato then prick with fork all over. Olive oil, garlic salt and medium chilli powder. Potatoes at room temperature. Blast them on top shelf, highest possible temperature for twenty minutes, then reduce to gas mark 5, middle shelf for an hour or so.
Crispy skin, fluffy middle.
My parents used to have an excellent metal skewer type thingy on an axis that you drove into the middle of each potato. Was brilliant, always perfect JPs.