Mackerel Cured in Olive Oil

Lay the mackerel in a single layer in an 11- or 12-inch skillet, preferably stainless steel.
The pan should be just big enough so that the fish fillets, nestled side by side, cover the bottom.
Pour 2 cups or more water and the lemon juice over the fillets to cover them, and sprinkle half the peppercorns and 1 teaspoon of the salt over.
Set the pan over medium heat, and bring to a slow rolling boil.
Turn down the heat, and simmer gently for 15 minutes.
Prop up a large wooden or plastic cutting board at a moderate angle, tipping toward the sink.
When the fillets are done (to check: the point of a knife should slip through the center easily), remove them carefully from the pan with a slotted spatula and lay them on the board.
Let them drain and cool completely.
Select a shallow glass or ceramic dish that will just hold the fillets in one layer, or you can use a smaller, slightly deeper dish that will accommodate two layers of fillets.
Arrange the mackerel in whichever dish, sprinkle each layer lightly with salt and the remaining peppercorns, and pour in enough of the olive oil to cover the fillets.
If you are using the mackerel the same day, let it marinate for 2 to 3 hours at room temperature.
Otherwise, cover securely with plastic wrap and store for up to a month in the refrigerator.
Bring back to room temperature 2 hours before serving.