Preheat oven to 425°. Toss grapes with rosemary, oil, vinegar, salt, and pepper.
Spread grapes on a baking sheet and roast 10 minutes. Turn over with a spatula and roast until very tender and slightly more shriveled, about 7 minutes more. Serve on a platter with cheese and toasts.
*Find at cheese shops, some grocery stores, and cowgirlcreamery.com