Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it lightly.
In a mixing bowl, mash the ripe bananas until smooth.
Add the peanut butter, eggs, vanilla extract, milk, and cinnamon to the mashed bananas. Mix well until all ingredients are fully combined.
Add in the flour, baking powder, baking soda, and salt. Mix until just combined.
Spoon the batter evenly into the prepared muffin tin, filling each cup about 3/4 full.
Bake for 12-15 minutes, or until the muffins are golden brown and a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for a few minutes before transferring them to a wire rack to cool completely.
Serve and enjoy!