Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9x5-inch loaf pan.
Mash bananas in a large bowl. Add flour, sugar, butter, egg, vanilla, baking soda, and baking powder; mix until well combined. Pour into the prepared loaf pan.
Bake in the preheated oven until a toothpick inserted into the center of loaf comes out clean, 50 to 60 minutes.
