A delicious first course or a side dish to roasted meats.
Put oven rack in upper third of oven and preheat oven to 425F.
Arrange radicchio wedges, cut sides up, in a 2 ½-quart shallow glass or ceramic baking dish (11 by 7 inches), then drizzle with oil and vinegar and sprinkle with salt and pepper.
Roast radicchio, turning over once or twice, until wilted and tender 30 to 40 minutes.
Arrange cheese over radicchio, then arrange prosciutto over cheese and roast until cheese is just melted 3 to 5 minutes. Serve immediately.