Heat the oven to 400°F and grease a 12-cup muffin pan (or line it with baking cups). Put the bananas in a large bowl and mash with a potato masher or fork. Add the yogurt, dates, prunes, oil, maple syrup, and vanilla, and stir to combine thoroughly. Stir in the baking soda and salt, and then stir in the wheat bran and whole-wheat pastry flour.
Divide the batter evenly among the muffin cups. Bake until the muffins are golden brown and a toothpick inserted into the center of one of them comes out clean, about 20 minutes. Serve the Healthy Bran Muffins warm.