01 - Preheat the oven to 350°F. Line a 12-cup muffin pan with paper liners or lightly grease with oil.
02 - In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon until evenly distributed.
03 - In a separate bowl, mash the bananas thoroughly. Add the sugar, oil, eggs, vanilla extract, and milk. Whisk until well combined and smooth.
04 - Pour the wet mixture into the dry ingredients. Stir gently with a spatula until just combined; do not overmix to keep the muffins tender.
05 - Gently fold the blueberries into the batter using a spatula, taking care not to crush them and distribute evenly.
06 - Divide the batter evenly among the prepared muffin cups, filling each about two-thirds full.
07 - Bake for 20 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
08 - Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely before serving.