Adjust oven rack to the center of the oven and preheat to 350°F / 177°C. Grease an 8.5x4.5 loaf pan and set aside.
In your bowl, mash your bananas. It helps to add the melted butter to make the mashing go quicker. When no large lumps of banana remains, add your eggs, vanilla, and brown sugar. Mix well.
Now add your gluten free flour blend, baking powder, baking soda, milk powder (if using), salt, and spices. Using a spatula, stir until thuroughly combined and no lumps remain, about 1 minute. Transfer batter to prepared pan and sprinkle the remaining sugar on top before baking.
Bake the banana bread for between 50 minutes to one hour, until a toothpick inserted in the center comes out clean. Let bread cool in pan on a wire rack for 10 minutes before removing from the loaf pan. After removing, let the bread rest for one hour before serving.