Potato gratin in a cast-iron pot – embers underneath and on the lid

Thin slices, warm cream and a modest bed of embers under the pot

4 servings
Difficulty: Medium
11 ingredients
15 steps

Photo: Guido Arnold, Wikimedia Commons (CC BY-SA 4.0)

Time: 20 min prep + 30–45 min for the embers + about 45–60 min in the pot (25–35 min if parboiled)

The lid is covered in embers that are slowly turning grey at the edges. Beneath it you can hear a low, thick bubbling – not the sharp sizzle of a frying pan, but the sound of cream thickening. When the lid is finally lifted aside, the steam comes first, then the smell of cheese and garlic, and the top has brown patches exactly where the embers lay thickest.

A potato gratin over the fire isn't a difficult dish, but it forgives few shortcuts. Thick slices never soften before the bottom has burnt, and cold cream means the pot sits waiting for half an hour before anything happens. Remember three words and it'll work: thin, warm, low. Thin slices, warm cream and only a few embers under the pot.

Have you made this recipe? Rate it

Be the first to rate this recipe.

More recipes to try

All recipes →

🔥 Over fire

Sockerkaka in a cast-iron pot – air under the tin, embers on the lid

🍽️ 4 servings 🥕 9 ingredients 👣 20 steps
🔥 Over fire

Fläskpannkaka over an open fire – Swedish oven pancake with pork belly, baked in a pot with embers on the lid

🍽️ 4 servings 🥕 7 ingredients 👣 10 steps
🔥 Over fire

Cast-iron chicken stew over an open fire

🍽️ 4 servings 🥕 11 ingredients 👣 8 steps
🔥 Over fire

Chorizo stew over an open fire – with a mild bowl for the children

🍽️ 4 servings 🥕 15 ingredients 👣 11 steps

Thin, warm, low

Thin. The slices should be two to three millimetres, about the thickness of a coin. That's the difference between an hour and nearly two over the embers. A mandoline gives even slices quickly, but it's the sharpest tool in the whole recipe, so use the guard or keep your fingers curled in. Don't rinse the slices. The starch left on them thickens the cream and binds the layers together.

Hot. Heat the cream and milk with garlic, salt and pepper until it steams and starts to move at the edge, but don't let it come to a full boil. If you pour warm liquid over the potatoes, the gratin starts cooking straight away instead of first having to warm up from cool-box temperature. It saves a quarter of an hour, sometimes more on a cold day.

Low. Cream and milk contain sugar and protein that burn onto hot iron long before the potatoes above are soft. The ember scales in the guide to cast-iron pot over a fire say roughly half underneath and half on the lid for a gratin. It's better to put a little less underneath than on the lid, in line with the guide's rule of thumb to choose the lid when in doubt, and to spread the embers in a ring rather than a heap right under the pot.

Cream and milk. Make at least half of the liquid cream. Whipping cream and medium-fat cream contain so little milk protein in relation to the fat that they can take long heating without splitting. Milk on its own, on the other hand, and especially skimmed milk or thin cooking cream, can curdle when it simmers for a long time with salt, onion and potatoes, and then the bottom turns grainy and watery. The liquid should come almost up to the top layer, not cover it. That way the top browns while the rest cooks in cream.

At home and by the fire

Parboiling at home halves the time. Heat the cream, milk and seasonings in a saucepan, add the thin slices and let them simmer gently for eight to ten minutes, stirring, until they're pliable but not falling apart. Then tip everything into two or three shallow tubs and cool them quickly, in a cold water bath in the sink, or outdoors if it's only a few degrees above freezing or colder, and then in the fridge. Only add the onion and cheese at the fire.

Why it has to be quick. Parboiled potato is starchy food. Bacterial spores that survive the boiling can germinate when the potatoes cool slowly, and the toxin they form doesn't go away when the gratin is reheated. So never let the parboiled slices sit and turn lukewarm in the saucepan, and transport them cold in the cool box. The same rule applies to the potatoes in baked potatoes in the embers. At the fire, the parboiled gratin must get piping hot all the way through, and for that 25–35 minutes is enough.

Raw potatoes at the fire. If you want to slice everything on site, only peel the potatoes at home if they'll be sliced within an hour, otherwise they'll turn grey. Bring a chopping board and put the slices straight into the pot.

The chilled items. Cream, milk and cheese are chilled foods. Keep them in the cool box with ice packs in the shade, and leave them out for no more than two hours in summer heat, and never in the sun. How to keep things apart, wash your hands and wash up without running water is explained in hygiene and washing up outdoors.

Safety at the gratin pot

A gratin holds its heat for a long time, and thick cream that spatters sticks to the skin. Lift the lid with a lid lifter and a fire glove, and open it so the steam goes away from your face. Dish up the gratin for the children and let it cool on the plate for a while – the middle is much hotter than the top.

If someone burns themselves: cool with cool water for about a quarter of an hour, no longer, and never with ice or snow. More about a safe zone around the fire can be found in fire safety in nature. If there's a fire ban, it's the decision of the county administrative board (länsstyrelsen) or the municipality that applies, see lighting fires outdoors. A pot with embers on the lid always belongs outdoors, never in a tent or an awning.

Green potatoes: cut away green or damaged parts with a good margin, and throw away potatoes that are green all the way through. For children under one year old, potatoes should always be peeled, which they already are here.

Allergens: the gratin contains milk in the cream, milk, cheese and butter. Lactose-free versions work the same way. Plant-based cooking cream is often thinner, so reduce the other liquid slightly.

Gratin with children

The gratin has plenty of jobs that don't involve heat. Children can scrub the potatoes, grate the cheese with an adult alongside and lay the slices like roof tiles in the cold pot, perhaps with their own pattern in the top layer. They can also sprinkle salt and cheese between the layers and keep an eye on the clock: every ten minutes it's time to turn.

The adults take care of the mandoline and the sharp knife, as well as the embers, the lifting and the saucepan of hot cream. Older children who are used to fires can push the skewer through the gratin once an adult has lifted the lid. More ways to divide up the jobs by age can be found in cooking with children over a fire.

Tips for potato gratin in a pot

The baking paper is an insurance policy. It removes most of the risk of a burnt bottom and makes the washing-up easy. Don't let it stick up over the rim, where it can catch fire and let ash in under the lid.
Two layers of potatoes on the bottom without cheese. The cheese burns most easily, so let the first layers be just potatoes and cream.
Rub the pot with garlic before the paper goes in, as in a French gratin, if you want more garlic flavour without the pieces.
The pot as an oven for something else. While the gratin rests, the same bed of embers is enough for meat or chicken. Whole chicken on a spit and gratin make a whole dinner.

Common mistakes

Thick slices. The top is done and the bottom burnt while the middle is still hard. Stick to two to three millimetres.
Too many embers underneath. It smells burnt after half an hour. Lift the pot off the bed of embers straight away, put the embers on the lid and let the residual heat do the work. Don't scrape up the burnt bits – serve from the top.
The middle is raw but the edge is done. Too much heat in too short a time. Remove some of the embers underneath, put the lid back on and give it another ten to fifteen minutes.
Pale top. The embers on the lid have turned grey. Put a thick layer of fresh embers on top for the last ten minutes.
Watery bottom. Mostly milk and too little cream, or rinsed slices. Let the gratin rest longer with the lid off so the liquid soaks in.
Parboiled slices that were left to cool slowly. Cool them quickly in shallow tubs and transport them cold.

Vary the potato gratin

Without cheese, as in France: just cream, milk, garlic and nutmeg. The top turns out paler and the flavour cleaner.
With leek or root vegetables: swap a third of the potatoes for thinly sliced parsnip or swede, or the onion for leek.
With anchovies: then you're getting close to Jansson's temptation, which also works in the same pot.
With smoked pork loin or ham: put diced smoked pork loin between the layers and the gratin becomes a dinner in its own right.

Frequently asked questions

How long does potato gratin take over an open fire?

About 45–60 minutes in a cast-iron pot with thinly sliced raw potatoes and pre-warmed cream, counted from when the pot goes on the embers. With slices parboiled in the cream at home, 25–35 minutes is enough. Cold cream and thick slices can drag the time out to nearly two hours.

How do you stop the gratin burning on the bottom?

Line the bottom with baking paper, put fewer embers under the pot than on the lid and spread them out in a ring. Start with a couple of layers of potatoes without cheese. If it smells burnt, lift the pot off the bed of embers and let the embers on the lid do the rest.

How do you know when the potato gratin is done?

A thin knife should go through all the layers in the middle without resistance. The bubbles at the edge should be thick and slow, the liquid should have sunk down and the cheese should have browned.

Can you parboil the potatoes for the gratin at home?

Yes. Simmer the thin slices in the cream for eight to ten minutes, cool them quickly in shallow tubs and put them in the fridge. Transport them cold in a cool box and heat the gratin until piping hot at the fire. Never let them cool slowly or sit lukewarm.

Can you use only milk in a potato gratin?

You can, but milk on its own can split when it simmers for a long time, and the gratin easily turns grainy and watery. Make at least half of the liquid whipping cream or medium-fat cream.

Potato gratin in a cast-iron pot – embers underneath and on the lid

Method

How to tell it's done