Ingredients

• 2 pounds Concord grapes (about 2 quarts), stemmed, divided
• 3/4 cup superfine granulated sugar
• Equipment: an ice cream maker

Instructions

1. Purée half of grapes in a blender until smooth, then force through a fine-mesh sieve into a bowl, discarding solids. Repeat with remaining grapes to yield 3 cups purée. Whisk in sugar until dissolved. Chill until very cold, 3 to 6 hours.
2. Freeze in ice cream maker, then transfer to an airtight container and put in freezer to firm up, at least 2 hours.