In a large bowl, add the peeled banana. Mash them well with a fork, but if you like them a little bit chunky, then just mash them coarsely.
Add butter, sugar, eggs, vanilla extract, milk and mix well.
Now add the salt, cinnamon, nutmeg, and baking soda, and then the all-purpose flour. Fold it all gently with the wet ingredients. Do not overmix.
Add the mini chocolate chips and mix. Save some to top in the baking pan.
Spoon the batter evenly into each muffin cup. Sprinkle some chocolate chips on the top.
Bake in preheated oven for 7 minutes then reduce oven temperature to 375 degrees and continue to bake 8-10 minutes until a toothpick inserted into center comes out clean.
Remove from muffin pan and let the muffins cool completely on a wire rack and enjoy! Store muffins in an airtight container.