Prepare the Filling:
In a bowl, mix the breadcrumbs with the grated parmesan, parsley, garlic, capers and black olives (if using). Season with salt and pepper.
Sardine Filling:
Place the sardine fillets on a work surface. If the fillets are very large, you can cut them in half.
Spread a little of the breadcrumb and cheese mixture on half of the sardine fillets. Cover with another fillet to close the filling.
Breading the Sardines:
Prepare three plates: one with flour, one with beaten egg and one with breadcrumbs.
Gently pass the sardines first in the flour, then in the beaten egg and finally in the breadcrumbs, pressing lightly to make the breading adhere well.
Frying:
Heat plenty of seed oil in a deep pan or in a deep fryer to 170-180°C. You can check the temperature of the oil with a kitchen thermometer or by placing a piece of breadcrumbs in the oil; if it sizzles immediately, the oil is ready.
Fry the sardines a few at a time to avoid lowering the temperature of the oil. Cook until golden brown, about 2-3 minutes per side.
