Take the sardines and remove the head of each one. Make a small incision along the belly of the fish from the neck down to the vent. Scoop out the intestines and discard them. Give the cleaned fish one final rinse to remove any stray scales or blood.
Cut the carrot lengthwise into quarters or halves. Slice these pieces crosswise into thin, uniform half-moon or quarter-moon shapes.
Take your two onions and slice them thinly.
Pour 50 ml of the olive oil into the bottom of a large, wide pot. arrange the cleaned sardines in a single layer over the base of the pot.
Distribute the sliced carrot and onions over the top of the sardines.
Sprinkle the fine salt, whole peppercorns, and mustard seeds over the layered fish, carrots, and onions. Also add 2-3 bay leaves.
Pour the wine vinegar and the remaining olive oil over the contents of the pot. Add the 1 litre of water.
Place the pot over medium-high heat until the liquid just begins to bubble. As soon as you see activity, reduce the heat to the absolute lowest setting.
Cover the pot and let the sardines simmer for two full hours.
After the two-hour simmer is complete, turn off the heat and let the pot cool completely to room temperature.
Once cooled, carefully transfer the preserved sardines, along with all the seasoned oil and vegetables, into clean, airtight jars or plastic food containers.
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Notes
Keep the containers in the refrigerator. The preserved sardines will taste incredible and remain safe to eat for up to two weeks.When transferring the cooked sardines to your storage jar, make sure they are completely submerged in the cooking liquid. If you need more liquid, top up the containers with fresh, good quality olive oil.Don't Rush: Resist the urge to turn up the heat or cut the time. The full two hours is essential for texture and safety.