Preparation Quarter tomatoes and in a food processor purée with sugar until smooth. Pour purée through a sieve, pressing hard on solids, into a shallow metal baking pan. Stir in pepper and vinegar until combined well. Freeze mixture, covered, stirring and crushing lumps with a fork about every 30 minutes, until no longer slushy but not frozen solid, 2 to 3 hours. Granita may be made 2 days ahead and frozen, covered. Just before serving, scrape granita with a fork to lighten texture and break up ice crystals.
Preparation Quarter tomatoes and in a food processor purée with sugar until smooth. Pour purée through a sieve, pressing hard on solids, into a shallow metal baking pan. Stir in pepper and vinegar until combined well. Freeze mixture, covered, stirring and crushing lumps with a fork about every 30 minutes, until no longer slushy but not frozen solid, 2 to 3 hours. Granita may be made 2 days ahead and frozen, covered. Just before serving, scrape granita with a fork to lighten texture and break up ice crystals.