I don't think they really eat broccoli rabe like this in Sicily, but having recently returned from a week of gorging myself on everything I could find on that pretty and olive-oil soaked island, I can tell you that the flavors represented in this dish—the sweet and sour of vinegar and sugar, the butteriness of pinenuts and olive oil—is about as Sicilian as it gets. Plus, "Sicilian Style Sweet and Sour Broccoli Rabe" just sounds sexier than "Not-Sicilian Broccoli Rabe with Sicilian-ish Flavors," doesn't it?
The root of the dish is a basic caponata, the Sicilian relish of eggplants cooked down in olive oil, flavored with capers, celery, onions, vinegar, and sugar. You'll see it most often in the U.S. as a dip, whereas in Sicily, it's a small plate unto itself served at the beginning and throughout the meal.
Here, I'm instead changing up the ratios a bit, thinning it out a little, and using it as a sauce for broccoli rabe. The bitterness of broccoli rabe adds yet another dimension to the already flavor-packed sauce.
The best part is how easy it is to put together. Once you have your sauce made and your broccoli rabe blanched, they can sit in the fridge for a day or two. All you have to do to serve is toss them together, and you're good to go.