Put about an inch of water in the bottom of your double boiler. Then set in the top pot of your double boiler and add 1 cup of water. Next, wash and quarter your apples and add them to the pot. Then wash your plums and slice around the circumference to split into two halves and remove the pits. Add them to the pot with your apples. Add the cinnamon sticks.
Cover and heat over high heat until the water in the bottom of your double boiler begins to boil, then turn to low. Allow to simmer for 1- ½ hours, stirring the fruit occasionally to help the softening process along.
Once the apples and plums are softened, discard the cinnamon sticks and run the fruit through a food mill or sauce master. Put the puree into a large bowl.
Stir in the sugar and nutmeg. Carefully pour into hot jars and use a non-metallic utensil to remove air bubbles. Affix lids and bands and process in a boiling water bath canner: 15 minutes for pints or 20 minutes for quarts. Remove to wire racks or layered towels to cool. Store in a cool, dry, dark place.
Recipe by Yellow Birch Hobby Farm at https://www.yellowbirchhobbyfarm.com/plum-applesauce/