I substituted all white whole wheat flour and about 1 tablespoon of corn starch for all flour because I don't have whole wheat pastry flour. I also added another 1/2 cup of blueberries. I mashed 3 large bananas which yielded a lot more than 1 cup. The additional volume did make it necessary to make more than 12 muffins. I ended up making 19. On some of them I topped with coarse turbinado sugar and cinnamon (about 1/4 teaspoon per muffin) and the rest I used a lime and powder sugar glaze. We prefer the cinnamon sugar combination. This is a great tasting and healthy. Very tender. I would definitely make these again. I did not miss the butter. Maybe next time I will add some vanilla. Thank you for a tasty recipe.