01 - Preheat oven to 350°F. Line a 12-cup muffin pan with paper liners or lightly grease each cup 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 ripe bananas until smooth. Add the sugar, vegetable oil, eggs, vanilla extract, and milk. Whisk until fully combined.
04 - Pour the wet mixture into the dry ingredients. Stir gently with a spatula until just combined, being careful not to overmix.
05 - Gently fold the blueberries into the batter using a spatula, distributing them evenly without crushing.
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 - Allow the muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely before serving.