Preheat the oven to 400°F. In a large bowl, combine both flours, the brown sugar, baking soda, salt, cinnamon, ginger, allspice and nutmeg. In another bowl, combine the eggs, pumpkin, bananas, buttermilk, oil and vanilla. Stir the wet mixture into the dry ingredients until just moistened.
Coat the muffin cups with cooking spray, then fill them three-quarters full with batter. Bake for 15 to 18 minutes or until a toothpick inserted in the center of a muffin comes out clean. Let the muffins cool in the pan for five minutes before removing them to wire racks. Ideally, serve the muffins while they're still warm.
