Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking dish.
In a large bowl, stir together the flour, sugar, artificial sweetener, baking powder and baking soda. In a separate bowl, stir together the butter, vanilla, milk, eggs and bananas; pour into the dry ingredients and mix well. Spread evenly in the prepared pan.
Bake for 35 minutes in the preheated oven, until a toothpick inserted in the center comes out clean.