Preheat oven to 350F.
In a large mixing bowl, whisk flour, baking soda, salt, nutmeg, and cinnamon. Set aside.
Mash bananas with a fork in Kitchenaid mixing bowl and mix in butter, both sugars, milk, egg, and vanilla. Stir until well combined.
Slowly add dry ingredients into mixing bowl and stir until just combined. Be careful not to over mix.
Fold in half the walnuts.
Spoon batter evenly into 12 muffin cups. Use liners for easy clean up.
Sprinkle remainder of walnuts over the batter.
Bake for 20 to 25 minutes or until the muffins are golden brown and a toothpick inserted into the center comes out clean.
Let rest for 5 minutes in the pan before removing to let cool completely on wire rack.