This recipe was developed in our school during "Slow Fish Week." It uses soffritto, but with a citrus twist to balance the oily fish. If you can't find fresh baby fennel, use a teaspoon of fennel seeds. Mackerel can also be cooked in this way.
Heat the oil in a frying pan over low heat and add the onion, celery, and carrot. Season with salt and pepper, to taste. Add the herbs, zest, fennel, and garlic and cook, stirring regularly, for 15 minutes. Remove and discard the herbs.
Preheat the oven to 350 degrees.
Lay each sardine skin side down on a board. Spread a little soffritto on each one and roll up. Arrange in an ovenproof dish and pour in any leftover soffritto or oil. Put into the oven until the sardines are cooked through, for 10-15 minutes. Serve with roast potatoes and sautéed spinach.