Janssons frestelse, or Jansson's temptation, is a traditional Swedish casserole dish made with julienned potatoes, onions, cream, and a special kind of canned pickled fish called Swedish anchovies. The ingredients are layered in a casserole, or other ovenproof dish, and baked in the oven until done. This dish is very popular in both Swedish and Finnish cuisines, and is commonly served as part of the traditional Christmas smorgasbord buffet or as a late night party snack. To give Janssons frestelse its characteristic flavor, it is very important to use only Swedish anchovies, called ansjovis, when preparing it. The origin of the name Janssons frestelse is not known with certainty, though the dish was possibly named either after a Swedish movie from 1921 by the same name or after a Swedish opera singer named Pelle Janzon.
The Swedish anchovies used in Janssons frestelse are not true anchovies at all, but a sardine-like fish called sprat. Sprats have a softer texture than anchovies, and are pickled using spiced, slightly sweet brine. It is essential to use Swedish anchovies for Janssons frestelse, not true anchovies, or the dish will taste quite differently. Swedish anchovies can be found in some European delis, specialty food stores, and are also commonly available in the food department of IKEA stores.
There are many different recipes for Janssons frestelse, but the essential ingredients and method of preparation remain the same. One traditional version of this recipe uses 2 pounds (1 kg) of floury potatoes, peeled and julienned into thin strips; one to three thinly sliced yellow onions; 1 1/2-2 cups (325-500 ml) cream; 7 ounces (200 g) Swedish anchovy fillets; dry breadcrumbs; butter; and black pepper. The onions are fried until softened, then layered in a buttered casserole dish with the potatoes and fish. The cream is poured over the dish, and freshly ground pepper and dry breadcrumbs are sprinkled on top, with some pats of butter. The dish is then baked at 430 degrees Fahrenheit (225 degrees Celsius) for about one hour, until the potatoes are cooked through and the top is browned.
Traditionally, Janssons frestelse is served at the table directly from the casserole, and cold beer is a common accompaniment. Janssons frestelse can be prepared ahead of time, either by assembling the dish and then baking it right before it is served or by baking it ahead of time and reheating before serving. The recipe for this dish was first published in 1940, and in Sweden the dish is often called simply "Janssons."