1. Preheat the oven to 350 degrees. Lightly grease muffin tin or line with cupcake liners.
2. In a large bowl, combine the flour, baking soda, salt, cinnamon and nutmeg.
3. In a separate bowl, mix the egg and brown sugar until smooth.
4. Add vanilla, melted butter, bananas, and milk to sugar mixture and whisk until thoroughly combined.
5. Pour liquid mixture into flour mixture and stir until just moistened, DO NOT overmix batter as this will result in tough muffins.
5. Fill each muffin cup 2/3 full with the batter. Sprinkle a generous amount of streusel topping over each of the muffins.
6. Bake muffins for 18-20 minutes or until muffins are golden. Remove muffins to a wire cooling rack.
1. In a small bowl, mix together with an electric mixer the brown sugar, flour, cinnamon, nutmeg, and butter to make the streusel topping. The mixture should reach a coarse consistency.