“I’m a Swede, I never buy potatoes in Ireland.”

So ran the subject line of an email I received a while back from a Swedish reader who was clearly very exercised by the all-too-frequent sight in of potatoes lying exposed to daylight in Irish shops. “Spuds should be kept in darkness,” he protested, “they develop poisonous solanine in daylight” and he was emphatic about not being prepared to buy potatoes thusly displayed at any price.

And my Scandinavian correspondent, I have to say, had a point.

And lo, exhibit A: Golden Wonders on display

Solanine, a bitter and toxic alkaloid, does occur naturally in potatoes – they are related to deadly nightshade, after all – though levels will vary depending on the potato’s variety and maturity. It doesn’t need light to form, but the rate of production of solanine in potatoes will increase with exposure to light and UV radiation, so it is always better for potatoes to spend their storage time in the dark. The greening you may see on potatoes – which results from the formation of chlorophyll and which also develops under daylight conditions – is an indication of increased levels of solanine, and I heed the advice from my Ma, who always told me to cut out the green bits of a spud (though the fact is that the average person would need to consume around 2lb of green potatoes in one sitting to be at risk of developing solanine poisoning). Even without greening, if a potato has developed a bitter taste, it’s another indicator of potential toxicity and, as your taste buds will probably tell you, you should steer clear.

Mostly of course, solanine levels in our spuds don’t get to poisonous levels – if they did, we, as a potato-eating nation, would surely know all about it. However, in the onward march of progress which has meant that we are now far more likely to bag a few well-lit roosters from the shelves of our local supermarket than to buy the ten stone sack of old, we are, in all likelihood, getting higher levels of solanine into the bargain. My reader is right to be disturbed by how we present our spuds for sale, and so should we be too. We owe a duty of care to our spuds and, more to the point, we owe a duty of care to ourselves.

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Jansson’s Temptation

Inspired by my Swedish correspondent’s concern for spuds, I thought it only proper to round things out, if not with some actual Swedish spuds then, at the very least, with a Swedish spud recipe. To be honest, I’ve had my eye on this traditional Swedish dish ever since I saw Donal Skehan prepare it on one of his Kitchen Hero TV shows. I was well pleased when I went along to the launch of his latest book this week – his third volume of recipes, no less – to find the recipe included.

You can think of it as a kind of Swedish take on gratin Dauphinoise, featuring matchstick potatoes, anchovies and onions baked in a mixture of cream and anchovy brine. It’s a wintry kind of dish, which is appropriate for the unseasonably cold weather with which our so-called summer has started. it goes without saying that, as is my wont, I have made a few slight adaptations:

– The recipe calls for Swedish anchovy fillets, which, the internet tells me are not, in fact, anchovies at all, but sprats, usually preserved in a liquid which is more sweet and aromatic than salty, and are somewhat like anchovy-sized rollmop herrings. Use them if you can find them – IKEA is probably a good bet for those of you not actually in Sweden – I used some Italian anchovies instead, ‘cos that’s what I had.

– I used about half the amount of onions called for in the original recipe – this is simply what felt right to me, but do add more onion if it’s to your taste.

– The original recipe calls for the addition of the anchovy brine to cream, though it doesn’t specify what volume of brine is used. I have specified the total volume of liquid that seems right to me for a gratin of this type, using a mixture of cream and whole milk, and to which you can add some of the anchovy brine to your taste.

– If your anchovies are stored in oil rather than brine, just add a tblsp or so of the oil to the gratin liquid, rather than the brine.

You’ll need:

• approx 700g potatoes, preferably a waxy variety
• 1 large onion, around 150g, peeled and sliced into fine half-moons
• 14-16 Swedish anchovy fillets (see notes above), brine reserved, or use 3-4 tblsp roughly chopped anchovy fillets or more to your taste
• 100ml single cream
• approx 250ml whole milk
• 1-2 tblsp butter
• small handful of fine breadcrumbs
• coarse salt
• freshly ground black pepper

You’ll also need:

• A large ovenproof dish, mine was around 20cm x 30cm and 4cm deep

The Steps:

• Preheat your oven to 220C.
• Scrub the potatoes, peel them or not as you prefer, and chop into fine matchsticks, around 2-3mm thick.
• Place half of the matchstick potatoes into your ovenproof dish, scatter over the sliced onions and the anchovies (either whole or roughly chopped, according to preference). Top with the remaining potatoes.
• Mix together the cream and milk, along with a couple of tblsp of reserved anchovy brine (or oil, if that’s what your anchovies were stored in). Pour approx. two thirds of this liquid over the potatoes, dot with the butter and sprinkle lightly with coarse salt and black pepper.
• Place in the oven for 20 minutes, then pour over the remaining cream and milk and press the mixture down with the back of a spoon (the liquid should come to slightly below the top of the potato mixture). Scatter with the breadcrumbs and return to the oven for a further 25-30 minutes or until the potatoes are tender and the top is golden brown. Serve with your choice of meats or fish or a just a crisp green salad, and enjoy.

The Variations:

• Donal notes that you can, of course, omit the anchovies and perhaps add some finely chopped garlic to this instead. I also quite fancy the idea of adding some capers and perhaps a touch of mustard, and of course you can vary the richness by adjusting the ratio of cream to milk to your taste.

The Results:

• Donal says this serves 8, which it should if you’re being reasonably restrained with your servings; count on 6 or so if the helpings are on the more generous side.