Preheat oven to 400°.
Combine first 8 ingredients in a large bowl. Stir in prunes; make a well in center of mixture. Combine buttermilk and next 5 ingredients (buttermilk through eggs); stir well with a whisk. Add to flour mixture, stirring just until moist. Spoon batter into 18 muffin cups coated with cooking spray.
Bake at 400° for 18 minutes or until done. Remove from pans immediately, and cool on a wire rack.