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1
Warm the olive oil in a wide pan over a medium flame, then add the breadcrumbs and stir continuously until every crumb is evenly golden and smells of toasted grain, so no pale or damp patches survive to turn the filling soggy inside the fish. Transfer immediately to a bowl the moment they reach a uniform amber — they will carry enough residual heat to darken further if left in the pan. The crumbs are ready when they release a dry, nutty fragrance throughout.
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2
Combine the toasted breadcrumbs with the drained currants, pine nuts, parsley, orange zest, and salt, and mix thoroughly so the currants are evenly distributed rather than clustered, which would give some rolls a burst of sweetness and others none. The stuffing should hold loosely together when pressed but not compact into a paste. It is ready when the mixture smells of citrus and toasted grain in equal measure.
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3
Lay each butterflied sardine skin-side down and place a generous spoonful of stuffing across the wider head end of the flesh, pressing it in firmly so it grips the fish rather than spilling when rolled. Roll from head to tail so the tail fin stands upright at the outside of each roll, giving the dish its characteristic silhouette and keeping the tail exposed to crisp in the oven. The roll must be tight and the stuffing genuinely generous — a thin, loose roll loses all character during baking.
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4
Oil the base of the baking dish, then stand the rolls upright and close together in a single layer, tails pointing up, packing them tightly so they support one another and cannot splay open during baking. Tuck a bay leaf between every two rolls so the leaf is in full contact with the fish and can release its resinous perfume directly into the flesh as it heats. The dish is correctly packed when no roll can fall sideways.
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5
Stir together the orange juice, vinegar, and sugar, then drizzle the olive oil over the assembled rolls and place the dish in an oven preheated to 180 °C. After ten minutes — once the rolls have set and will not be disturbed by the liquid — pour the agrodolce sauce evenly over them and return the dish to the oven for a further eight to ten minutes, so the sauce reduces into the fish rather than simply steaming around it. The rolls are done when the exposed tail tips are lightly crisped, the tops are golden, and the sauce has reduced to a fragrant, slightly syrupy glaze visible at the base of the dish.
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6
Remove from the oven and leave the rolls in the dish to cool to room temperature, so the agrodolce sauce is drawn back into the flesh as it rests and the sweet-sour perfume of orange and vinegar rounds out rather than biting sharply on the palate. Do not serve hot — this integration takes at least twenty minutes of resting. The dish is ready when the sauce has been absorbed into the rolls and the orange and vinegar are present on the nose without sharpness.