Preheat oven to 375ºF. Grease a standard 12-cup muffin pan or use paper liners.
In a bowl whisk together flour, nutmeg and baking soda.
In another bowl, cream margarine and sugar. Add mashed banana and egg.
Add dry ingredients to banana mixture. Add chocolate chips (if using).
Mix and pour into prepared muffing pan. Sprinkle with coarse sugar (if using). Bake for 23-28 minutes.