Preheat your oven to 350°F (175°C).
Line your muffin tin with parchment paper liners or grease it lightly.
Mash the very ripe bananas until smooth, about 1 1/2 cups.
Add eggs, softened butter, brown sugar, milk, and vanilla to the mashed bananas. Whisk until combined.
In a separate bowl, whisk together gluten-free flour, baking powder, baking soda, and salt.
Gradually add dry ingredients to wet ingredients, folding until just combined.
Fold in chocolate chips or other add-ins.
Spoon batter into prepared muffin tin, filling each cup about 2/3 full.
Bake for 18-22 minutes, or until a toothpick comes out clean.
Cool in the tin for 5 minutes before transferring to a wire rack.