Preheat oven to 350°F. Spray a 9x5-inch loaf pan with cooking spray (or grease with shortening or butter) and set aside.
In a large bowl, combine and mash together the melted butter and bananas. Add the eggs and vanilla extract and continue to mash and combine the ingredients until everything is well combined.
In a medium bowl, whisk together the flour, sugar, baking soda, salt, and cinnamon. Add the flour mixture to the banana mixture and stir just until smooth.
Spread the batter evenly into the prepared pan.
Bake for 45-55 minutes or until a toothpick inserted near the center of the loaf comes out clean.
Cool loaf in pan for 10 minutes before removing to a wire rack to cool completely.
Notes
Try adding 1/2 to 1 cup chopped walnuts or chocolate chips to the bread batter before baking.
Prefer muffins? You can use a standard-size muffin tin and bake them for about 25 minutes. Again, use a toothpick to check for doneness.