When we were in Venice, Italy, where you are supposed to enjoy the seafood, we had a dish of
Sweet and Sour Sardines which the recipe in the link identifies as one of the most typical Venice dishes. And it was delicious. It was one of the first I tried to recreate when I got home. The recipe I worked from was
this one. Unfortunately for me, I had trouble finding fresh sardines. The first time I tried it, I used canned, skinless, boneless sardines. And it was good. But I liked the onions best. The second time I tried it, the store didn't have sardines but said smelt would be close. Again, it was good. But I liked the onions best.
I finally decided it wasn't the fish, it was the onions. If you search for sweet and sour sardines or "Sarde in Saor", you'll find plenty of recipes. I used the
one I originally found as my starting point. Without the sardines. And I changed up the quantities. I was quadrupling the recipe but I still only used 1/4 C raisins and 1/4 C nuts. You can adjust to your tastes. I discovered that there was too much oil for me so I cut that way back. The end result is sweet caramelized onions that have the tang of vinegar with some raisins and pine nuts. And the longer they sit in your fridge, the better they taste. My problem is letting them sit at all. They are good all by themselves or with any kind of fish. Today I had them with baked salmon. I've also had them with sautéed tilapia. I'm sure you can find other things to serve them with.
Before cooking the onions, soak about 1/4 C raisins in 1/2 C white wine. And toast about 1/4 C of pine nuts.
I used 4 large sweet onions. I cut the top of the onion off - the part that sprouts. Then I cut the onion in half through the root. I put the halves cut side down, cut off the root, and then sliced them thinly. If I followed the recipe I would then cook those onions in 3 cups of olive oil. DON'T do that. I heated about 2 T of olive oil in my 10 inch frying pan and tossed in the onions. I let them cook down, removing some of the liquid as they cooked. When it seemed like they might stick, I added a little bit more olive oil. Then I just let them cook until they became nice and brown. I didn't time it but my best guess is 45 minutes.
Add the white wine vinegar, raisins, and nuts and salt to taste. I also tossed in the wine the raisins were soaking in. Then cook it a little longer to let some of the juice evaporate. Put it in a bowl, let it cool and then put it in the refrigerator and try not to eat it until the next day.