Preheat your oven to 350°F. Line a muffin tin with cupcake liners or spray it well with non-stick baking spray.
Peel and mash the bananas in a bowl using a fork until creamy. You can leave a few chunks if you like some texture.
In a small bowl, crack and lightly beat the eggs with a fork.
In a large mixing bowl, combine the flour and butter. use and hand mixer or stand mixer on low speed until the mixture has a sandy texture.
Add the salt, baking powder, and baking soda. Stir to combine.
Add the brown sugar, vanilla extract, beaten eggs, and mashed bananas to the bowl.
Stir everything with a wooden spoon until just combined. Stop mixing as soon as the batter comes together to avoid overmixing.
Let the batter rest in the refrigerator for 30 minutes to 1 hour to hydrate the flour and create a more tender muffin. ( You can skip this step if you're short on time.)
Scoop the batter evenly into your prepared muffin tin.
Bake for 45 to 60 minutes, depending on your oven and how much banana you used. The muffins are done when a toothpick inserted in the center comes out clean and the tops are golden brown.
Let the muffins cool in the pan for 10 minutes. Then transfer them to a wire rack to cool completely.