Preheat your oven to 350°F (175°C). Grease or line a 9x5 loaf pan.
In a large bowl, mash the ripe bananas until smooth.
Add sugar, eggs, melted butter, and vanilla extract. Mix until combined.
In a separate bowl, whisk together flour, cinnamon, baking soda, and salt.
Gradually add the dry ingredients into the banana mixture. Stir gently.
Fold in mini marshmallows (optional but recommended for extra gooey texture).
Pour the batter into the prepared pan and smooth the top.
Bake for 50–60 minutes, or until a toothpick comes out clean. Let cool before slicing.