Start by preheating your oven to 425°F (220°C). While it's heating up, line a muffin tin with muffin liners.
In a large mixing bowl, mash the ripe bananas until they're smooth.
If you're adding any optional mix-ins like chocolate chips, peanut butter chips, or walnuts, gently fold them in now.
Fill each muffin liner about 3/4 full with batter.