My recipe has now been taken over by the chef and management of a 5 star hotel for the evening buffet after tasting.
Pat dry the washed sardines, which have been cleaned ready for use, and season the outside and inside with salt and pepper. Flour carefully
Heat a good dash of oil in a pan and fry the saardines nice and brown on each side, not too hot. Put the fried ones aside to cool off. When all the fish are cooked through, bring all the ingredients (except the onions) to the boil in the same pan and let them simmer on a low flame for about 19 minutes.
Briefly blanch the onions in the stock and remove the pan from the heat. In a suitable container, cover the bottom with a layer of the onion spice mixture and always layer the fish in layers covered with the onions and spices.
Finally, season the acidic broth to taste and pour it over the fish. The fish must be completely covered with the stock. We let them sit for 10 days (without trying). The longer you leave them alone, the better they get.
If the brew is not quite enough, you can make do with fish stock and dark balsamic vinegar.