Preheat the oven to 400 degrees F. Spray a 12 cup muffin tin with nonstick spray. You'll have some extra batter though, so you can spray a second pan (3 or 4 cups) with nonstick spray, or make a few mini muffins instead.
In a medium bowl, whisk together the buttermilk, sugar, applesauce, eggs and bananas. In a separate medium bowl, whisk together the flours, baking powder, cinnamon, baking soda, salt and nutmeg. Add the dry ingredients to the wet ingredients and carefully stir with a rubber spatula until all is just about combined. Carefully stir in 1 cup blueberries.
Use an ice cream scoop or ⅓ cup measuring cup to portion the batter into the muffin cups. Sprinkle the tops of the batter with the remaining blueberries.
Bake until a toothpick inserted in the center comes out clean, 20 to 25 minutes. Cool for a bit, and then eat!