Heat oven to 400 degrees F (205 degrees C). Grease bottoms only of 12 muffin cups or line with baking cups.
In a medium bowl, combine flours, baking powder, baking soda, cinnamon, and salt; mix well. In a small bowl, lemon juice, plum puree, oil, and egg; blend well. Add dry ingredients all at once; stir just until dry ingredients are moistened (batter will be lumpy.) Stir in chopped apples.
Fill cups 2/3 full. Bake for 18 to 22 minutes or until toothpick inserted in center comes out clean. Cool 1 minute before removing from pan. Serve warm.
To Make Cooked Plum Puree
1. Cut and puree fresh plums with 1 teaspoon lemon juice for every 10 or so plums
2. Cook on medium head until bubbles begin to form.
3. Turn to low and simmer for 15-45 minutes (the longer the thicker and more consentrated the plum)