Jansson's temptation potato and anchovy gratin (Janssons frestelse)

1. Peel the potatoes and cut them into 5 mm thick batons; slice the onions into thin half-rings.

2. Soften the onions in 1 tbsp butter for 5 minutes without browning.

3. Layer half the potatoes, the onions and the fish fillets in a buttered ovenproof dish, then the remaining potatoes; drizzle over the brine from the fillets and season lightly with pepper.

4. Pour over half the cream, sprinkle the top with breadcrumbs and dot with the remaining butter.

5. Bake in an oven preheated to 200 °C for 20 minutes, then pour over the rest of the cream and bake for another 30-35 minutes until the potatoes are tender and the top is golden.

6. Let it rest for 10 minutes and serve warm.

Tip: No Swedish Christmas smörgåsbord is complete without Janssons frestelse, "Jansson's temptation". Swedish "ansjovis" are actually sprats cured in a sweet-spiced brine, not anchovies; elsewhere you can use anchovy fillets, but use fewer because they are saltier, and don't add extra salt. Cutting the potatoes into batons matters: the starch they release thickens the cream and makes the gratin really creamy.