Preheat your oven to 325°F (165°C) and grease a standard-sized bread pan.
In a mixing bowl, cream together the mashed bananas, shortening, sugar, eggs, milk, and vanilla extract until well combined.
In a different bowl, mix together the flour, baking soda, and baking powder.
Gradually add the dry ingredients to the creamed mixture, mixing until just combined. Be careful not to overmix, as this can result in a tougher texture.
Pour the batter into the prepared bread pan, spreading it evenly.
Bake in the preheated oven for about 60 minutes or until a toothpick inserted into the center comes out clean.
Once baked, allow the banana bread to cool in the pan for a few minutes before transferring it to a wire rack to cool completely.