Preheat oven to 375°F | 190°C.Line 12 muffin cups with cupcake papers and/or spray with baking spray.
In a medium bowl, whisk together dry ingredients: flour, baking soda, baking powder, cinnamon, and salt.
In a large bowl, stir bananas, sugar, egg, and applesauce until evenly mixed.
Using a spatula, fold the wet ingredient mixture into the dry mixture, mixing only no more dry flour is visible. The batter will be a little lumpy and about the same consistency as thick cake batter. Do not over mix.
Stir the blueberries into the batter.
Spoon batter into prepared muffin cups. Sprinkle the top of each muffin with about 1 teaspoon of Demerara sugar.
Bake in preheated oven for 18 to 20 minutes, until a toothpick inserted into center of a muffin comes out clean.
Remove muffins from tin and allow to cool on wire rack.
Notes
These muffins freeze well, so make a couple of batches to keep on hand for a fast, easy breakfast or snack.