Juicy blackberries, raspberries, plums, and blueberries can be enjoyed even after they've disappeared from summer markets. The fruits are swirled with vanilla yogurt and a shot of lemon or lime juice to form these tart architectural icies.
Place plums or 2 1/2 pints raspberries in the jar of a blender or the bowl of a food processor. Pulse briefly, then puree until nearly liquid, about 1 minute. For plum pops: Pass puree through large-mesh sieve to remove skin. For raspberry pops: Pass puree through a very fine sieve to remove seeds; you should end up with 1/2 cup. Add 1 tablespoon lemon juice, and blend.
Rinse out blender jar, and blend yogurt with remaining tablespoon lemon juice until smooth.
Layer each 1/3-cup pop mold with yogurt and puree, adding rest of raspberries along the way. Swirl mixtures together with knife.
Let freeze 25 minutes. Insert wooden pop sticks halfway, and freeze overnight.
Pops will keep, frozen, for at least 3 weeks.