Preheat oven to 350°F (177°C)
Grease bread loaf pan with butter or cooking oil spray.
In a large mixing bowl, combine all dry ingredients: flour, sugar, baking soda, baking powder, and salt. Mix well. Set aside.
Peel the bananas and put them in another large or medium mixing bowl. Mash. Add the butter and eggs. Mix well.
Combine the wet ingredients into the bowl of dry ingredients. Mix gently.
Pour the batter into the bread loaf pan. Bake 350°F for an hour. Insert a toothpick in the middle of the loaf. If the toothpick comes out clean, it is done. Add another 10-20 minutes if not done.
Remove from the oven. Let it cool down for 30 minutes before removing from the pan.