3 McIntosh apples (1 1/2 pounds), quartered and cored
3 Paula Red, Northern Spy or Empire apples (1 1/2 pounds), quartered and
3 black plums or large Italian prune plums (10 ounces), halved and pitted
6 cups water
1/3 cup sugar
1 tablespoon fresh lemon juice
1/2 teaspoon cinnamon
Pinch of freshly grated nutmeg
In a large saucepan, cover the apples and the plums with the water and bring to a simmer. Cover and cook over low heat until the apples and plums break down, about 5 minutes. Drain the fruit in a fine sieve set over a bowl; reserve 2 tablespoons of the cooking liquid in a small bowl. Using a wooden spoon, press the fruit through the sieve into the bowl to make a fine puree. Discard the skins.
In a large saucepan, combine the apple-plum puree with the sugar, lemon juice, cinnamon and nutmeg. Simmer the puree over moderately low heat, stirring frequently, until the sugar dissolves, about 3 minutes. Stir in the reserved 2 tablespoons of cooking liquid. Scrape the applesauce into a bowl, cover and refrigerate for 1 hour, until chilled.
The applesauce can be refrigerated in an airtight container for up to 4 days or frozen for up to 3 months; thaw in the refrigerator before serving.