Preheat oven to 325 degrees F (165 degrees C). Grease a 9x5-inch loaf pan.
Combine bananas, sugar, egg, and butter together in a bowl. Mix flour and baking soda together in a separate bowl; stir into banana mixture until batter is just mixed. Stir salt into batter. Pour batter into the prepared loaf pan.
Bake in the preheated oven until a toothpick inserted in the center of the bread comes out clean, about 1 hour.