Foil is the whole problem
It is on about half the recipes for a baked potato and it does the exact opposite of what people think it does. Understanding why makes the rest of the method obvious rather than a list of tips.
A crisp skin is a dry skin. Nothing else. As a potato bakes in a hot dry oven, moisture leaves the surface, the skin contracts and hardens, and you get that thin brittle shell that is the entire reason for baking one instead of boiling it.
Wrap it in foil and the moisture has nowhere to go. It condenses on the inside of the foil, runs back down and sits against the skin for ninety minutes, so the skin cooks in steam. The potato inside is perfectly good. The skin is soft, pale and slightly wet, and you have made a boiled potato with extra steps.
Foil has one legitimate use here, which is wrapping a finished potato to keep it hot on the way somewhere. Never before.
Everything else follows from that one idea
Once you know the skin crisps by drying, the rest of the method stops being a list and becomes obvious.
Dry the potato before it goes in. A wet skin has to lose that water before it can start losing its own, so the first twenty minutes of the bake are spent evaporating washing-up water. A tea towel costs nothing.
Salt it. Salt pulls moisture out of the skin by osmosis, which is the same job the oven is doing, from the other side. Flakes rather than fine salt, because flakes sit on the surface rather than dissolving straight into it.
A thin rub of oil. Oil conducts heat into the skin far better than air does, so the surface gets hotter and browns rather than merely drying. A teaspoon between four. A potato drowning in oil fries in patches and goes hard instead of crisp.
Straight onto the shelf, not into a tin. Air has to circulate all the way round. A potato sitting in a roasting tin has one face in a pool of its own steam, and that face is soft when it comes out.
Ninety minutes is ninety minutes
There is no version of this in a conventional oven that takes forty. What you are waiting for is heat reaching the centre and staying there long enough for the starch granules to absorb water and burst, which is what fluffy is, and heat moves through a potato at the rate it moves through a potato.
Test with a skewer rather than a clock. It should go into the middle and meet nothing at all, and the skin should look visibly dry and slightly wrinkled. A potato that is done on the outside and firm in the middle is the standard failure, and it is usually a very large potato and an optimistic timer.
The one shortcut worth knowing is a split method: ten minutes in the microwave to get heat into the centre, then twenty five in a hot oven to dry and crisp the skin. That gets you most of the way in a third of the time. A microwave on its own gets you a good interior in a leathery bag, which is the trade people make on a weeknight and then feel slightly sad about.
Squeeze it, do not cut it in half
Cut a cross in the top and push the two ends towards each other, and the flesh pushes up through the cross in a mound. Halving it lengthways gives you two flat pieces with the filling sliding off them, which is worse in a way that is hard to articulate until you have done it both ways.
Fork the inside up as soon as it is open. Steam escapes, the flesh stays loose, and the bottom half does not compress into a dense layer while the plate sits waiting. Butter immediately, before anything else, so it melts down into the potato rather than sitting on top of a pile of cheese.
It is a plate rather than a recipe
The beans and cheese here are one answer and not the only one. A baked potato is a base for anything with a sauce, which makes it the most useful leftover vehicle in the kitchen: last night's chilli, the end of a bolognese, tuna and mayonnaise, or the last of a casserole that would not feed four again on its own.
That is worth planning around rather than discovering. Four potatoes cost almost nothing and take ninety minutes of oven time that needs no attention, so putting them in when you are already cooking something else is close to free.
Common questions
Should you wrap a baked potato in foil?
No, and it is the single thing that ruins one. A crisp skin is a dried skin, and drying means moisture leaving the potato and going into the oven. Foil traps that moisture against the surface, where it condenses and cooks the skin in its own steam. What comes out is a boiled potato in a foil jacket, with a skin that is soft and slightly damp. Foil is useful for keeping a cooked potato hot and for nothing before that.
How long does a baked potato take?
About ninety minutes at 220°C for a large one, and it is not a time you can shorten in a conventional oven without paying for it. What you are waiting for is the inside reaching the point where the starch granules have absorbed water and burst, which is what fluffy means, and that takes as long as it takes for heat to travel to the centre. Test with a skewer rather than a clock: it should meet no resistance at all.
Can you cook a baked potato in the microwave?
You can cook one, and you cannot bake one. A microwave heats the water inside the potato, so the inside cooks beautifully and fast, and the skin never dries out because nothing is drawing moisture off the surface. The result is a good potato in a leathery bag. The honest compromise is ten minutes in the microwave followed by twenty five in a hot oven, which gets you most of the skin for a third of the time.
Why do you prick a potato before baking?
Because it is a sealed bag of water and steam has to get out. Most of the time nothing happens, which is why people stop bothering, and occasionally one bursts in the oven, which is loud and takes twenty minutes to clean off the roof of the oven. Four or five holes with a fork is the whole job. The advice about it drying the potato out is not really true at this scale.
What potatoes are best for baking?
A floury one, large. Maris Piper and King Edward in Britain, russet in America, or anything sold specifically as a baking potato. Floury varieties carry more starch and less water, and it is the starch swelling that gives you the fluffy interior. Waxy potatoes are bred to hold their shape, which is exactly what you do not want here, and they come out dense however long you bake them.
Why put salt on the skin of a baked potato?
Two reasons and both are real. Salt draws moisture out of the skin by osmosis, which helps it dry and crisp, so it is doing part of the same job the dry oven does. And the skin is the part with the most flavour and the most texture, so seasoning it directly puts salt where people actually taste it. Flakes work better than fine salt because they stick rather than dissolving straight in.
Should you oil a baked potato?
A thin rub, yes. Oil conducts heat into the skin better than air does, so the surface gets hotter and browns rather than just drying, and it helps the salt stick. What it does not need is a coating: a potato swimming in oil effectively fries in patches and the skin goes hard rather than crisp. A teaspoon between four is plenty.
How do you reheat a baked potato?
Twenty minutes at 200°C, which brings the skin back. The microwave is faster and turns a crisp skin soft, which is the whole thing you spent ninety minutes on. They keep two days in the fridge cooked and they do not freeze: the flesh goes watery as the ice crystals break the cell walls, and the skin never comes back at all.