Preheat oven to 350 degrees. Place muffin cups in muffin tins.
Mix sugar, applesauce, and egg until creamy and light yellow. Add bananas and vanilla. Add flour, cocoa, baking soda, and salt. Stir until smooth. Spoon the batter into the muffin tins. Top with course sugar if desired.
Bake for 20-25 minutes, until toothpick poked in center muffin comes out clean.