Preheat oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a large bowl, cream together butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla. Mix in mashed bananas.
In a separate bowl, whisk together flour, baking soda, baking powder, cinnamon, and salt. Stir the dry ingredients into the banana mixture until just blended.
Spread batter into the prepared pan. Sprinkle with chopped walnuts, if desired. Bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Allow cake to cool in pan for 10 minutes, then turn out onto a wire rack and cool completely.
Interesting Facts
Bananas are a great source of vitamin B6, vitamin C, and potassium.
This cake can be served as a snack or as a dessert.
This cake can be stored in an airtight container in the refrigerator for up to 5 days.