Finely chop the parsley and set it aside.
Slice the onions, making 2 mm (1/16") thick slices.
Put the onions inside a pan with fast boiling water.
Leave the onions to boil for 3 or 4 minutes. This will tenderise the onion and also will help to take away part of their strong flavour.
After 3 or 4 minutes of boiling, refresh the onion under cold water (to stop them cooking), then drain them.
Put the onions in a large container to rest.
Next, take as many sardine or anchovy fillets (I used both) as you like and lay them down onto kitchen paper.
Gently pat them with kitchen paper to remove excess oil from the jar or can (usually sunflower oil).
Take a deep dish and generously pour in some good quality extra virgin olive oil.
I have two dishes because one is for the anchovy fillets and one for the sardine fillets.
Now, spread the onions into the dishes.
In each dish add 30 ml (1/8 cup) of red wine vinegar.
Add few drops of good quality balsamic vinegar into the dishes.
Season with pepper.
Season with salt.
Add the fillets into the dishes.
Garnish with parsley.
Using two large spoons, gently mix all the ingredients. If using sardine fillets, be very gentle and try not to break them. The picture shows the oval dish with the sardine fillets and the square one with anchovy fillets.
I like to serve this dish on grilled slices of Italian country loaf.
Finally, a “crostone” (large slice of grilled bread) topped with the recipe.