Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Combine the flour, baking soda and salt; stir into the batter until blended. Fold in the bananas and walnuts (if desired). Spread evenly into the prepared pan.
Bake for 30 to 40 minutes in the preheated oven. Cake is done when it springs back to the touch.
Let cool in pan for 10 minutes, then turn out onto a wire rack and cool completely.
Interesting Facts
Bananas are native to Southeast Asia and Australia.
Bananas come in many varieties and sizes, from small finger bananas to large plantains.
Bananas are an excellent source of potassium and fiber.