Preheat your oven to 350°F (175°C).
Line a muffin tin with paper liners or lightly grease it.
Mash the very ripe bananas in a large mixing bowl until smooth.
Add the softened butter, brown sugar, eggs, milk, and vanilla extract to the mashed bananas and mix well.
In a separate bowl, whisk together the gluten-free flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet banana mixture, stirring just until combined.
Gently fold in the chocolate chips or your choice of add-ins.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake for 18-22 minutes, or until a toothpick inserted comes out clean.
Let the muffins cool in the pan for about 5 minutes, then transfer to a cooling rack.