In a medium saucepan over medium heat, combine apples, pears, sugar and 1/2 cup water; cover. Cook until tender, about 10 minutes. Press mixture through a sieve placed over a bowl. Discard apple and pear skins and stir in apple juice and another 1/2 cup water. Place mixture in a food processor and pulse 3-4 times until any big chunks are smooth.
If making without an ice cream machine, pour into a shallow container and freeze 6 hours, scraping with a fork once or twice to break up crystals. If using a machine, churn until firm enough to scoop.