Chop finely the onion then gently brown it in extra virgin olive oil until golden. Add the roughly chopped preserved sardines and cook for 2 minutes then add the breadcrumbs and stir fry until the bread is golden brown
Chop parsley, pine kernels, raisins and fennel seeds. Add them to the onion and anchovies. Add salt and pepper.
The filling should be not too dry. If it is too dry, simply add fresh extra virgin olive oil. Otherwise, if the filling is too liquid, just add more breadcrumbs.
Once the filling is ready, open the sardines and take ou the internal fishbones.
Pre-heat the oven at 180 degrees. Place on a tray a bit of extra virigin olive oil, then add the bay leaves. Place one sardines with the skin facing the tray and place some filling on top of it. Cover with another sardine (like a sandwich) with the skin not facing the filling.
Cook in the oven for 30 minutes.