Preheat oven to 375˚F. Fill a large bowl with cold water and ice cubes, and set aside. Bring a pot of water to a boil and blanch the cipolloni for just 10 seconds. With a slotted spoon, transfer them to the ice water bath and submerge until cool enough to handle. Use a sharp knife to make a small slit in each one, then remove the outer layer.

Arrange the peeled onions and tomatoes in a single layer in a roasting pan. Toss in olive oil and sprinkle with a generous pinch of salt. Roast for 45 minutes, gently turning the tomatoes and onions every 15 minutes or so. A few minutes before taking the tomatoes and onions out, place teh slices of bread directly on the oven rack for a minute or 2, until lightly toasted.

Transfer the toasted bread to a serving platter, arranging the slices side by side. Spoon the white beans over the toasted bread, then top with the roasted tomatoes and cipollini. Be sure to scrape the entire contents of the roasting pan, especially the juices, over the bread. Sprinkle with fresh basil, then serve.