Janssons's temptation is a classic Swedish casserole of layered potatoes, onions, pickled sprats, bread crumbs and cream.
Rinse the potatoes in cold water to eliminate starch.
Heat oven to 390-400º F. Butter an oven dish.
Mix the liquid from the pickled fish with the cream and milk. Season with salt if needed.
Spread half the potatoes in the buttered dish. Layer first the onions and then the fish on top. Finish with the rest of the potatoes.
Pour the liquid evenly over the top. Sprinkle with bread crumbs and dot with butter.
Bake until golden brown, 45-60 minutes.
Remove from the oven, let it rest a few minutes and serve.
Pickled sprats can be substituted with pickled herring.