Preheat oven to 350 degrees F. Line a standard-size muffin pan with paper liners or spray with non-stick cooking spray; set aside.
Sift together the flour, baking soda, salt and nutmeg into a large bowl.
In a separate medium bowl, whisk together the mashed bananas, both sugars, butter, milk and egg. Pour over the dry ingredients and fold to combine. Add half of the chopped macadamia nuts to the batter and fold gently to combine.
Divide the batter evenly between the muffin cups. Sprinkle the tops with the remaining chopped macadamia nuts.
Bake until golden brown and a thing knife inserted into the center comes out clean, about 25 minutes. Let cool in the muffin pan for about 10 minutes, then remove to a wire rack to cool completely. Store muffins at room temperature for up to 3 days.