Soak raisins in dry white wine for 30 minutes to one hour.
Heat olive oil in a skillet over medium heat. Add onions and fry until brown. Add raisins and wine along with cloves and white wine vinegar. Cook for eight to ten minutes until liquid has reduced to one quarter. Remove from heat.
Toss flour with salt and pepper. Pat sardines dry of moisture with a paper towel and lightly dredge with flour. In a skillet, heat vegetable oil for shallow frying. When oil is shimmering, fry sardines in batches until golden brown. Drain on paper towel before transferring to a baking dish, ensuring they are in one layer. Pour sweet and sour sauce over sardines and chill in the refrigerator for at least three hours.
Serve sprinkled with toasted pine nuts, chopped Italian parsley, and lemon slices.
