Pomegranate Gelato

Whisk together cream, milk, sugar, cornstarch, and salt in a 2 1/2- to 3-quart heavy saucepan. Bring to a boil over moderate heat, whisking occasionally, then boil, whisking, 2 minutes. Remove from heat and whisk in remaining ingredients. Transfer to a bowl and chill, uncovered, until cold, at least 1 hour. Freeze in ice cream maker, then transfer to an airtight container and put in freezer to harden, at least 2 hours. Soften gelato slightly in refrigerator, about 20 minutes, before serving.