Preheat the oven to 375°F (190°C) and line a muffin tin with paper liners.

In a mixing bowl, whisk together the mashed bananas, granulated sugar, melted butter, egg, and vanilla extract until well combined.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix.

Gently fold in the fresh blueberries until they are evenly distributed throughout the batter.

Divide the batter evenly among the prepared muffin cups, filling each one about three-quarters full.

If desired, sprinkle a pinch of brown sugar or turbinado on top of each muffin for a caramelized finish.

Bake the muffins in the preheated oven for 18-20 minutes or until a toothpick inserted in the center comes out clean.

Remove the muffins from the oven and let them cool in the muffin tin for a few minutes before transferring them to a wire rack to cool completely.