Step 1: Preheat your oven to 350°F (175°C) and grease a 4x8-inch loaf pan with butter or non-stick spray.
Step 2: In a large mixing bowl, mash the ripe bananas with a fork until smooth or slightly chunky according to your preference.
Step 3: Stir the melted butter into the mashed bananas until well combined.
Step 4: Mix in the granulated sugar, beaten egg, and vanilla extract.
Step 5: Sprinkle the baking soda, salt, and cinnamon over the wet mixture and stir to incorporate.
Step 6: Gently fold in the all-purpose flour. Stir just until the flour is no longer visible; do not over-mix.
Step 7: Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Step 8: Bake for 50 to 60 minutes, or until a toothpick inserted into the center comes out clean.
Step 9: Remove from the oven and let the bread cool in the pan for 10 minutes before transferring to a wire rack to cool completely.