Preheat your oven to 350°F (175°C).

Grease a 9x13 inch baking pan generously with unsalted butter or use a non-stick spray.

In a mixing bowl, whisk together the flour, baking soda, and baking powder.

In a large mixing bowl, beat together the softened butter and granulated sugar until light and fluffy.

Add eggs, one at a time, to the butter mixture, mixing well after each addition, then mash and mix in the ripe bananas.

Gradually mix the dry ingredients into the wet batter until just combined, then fold in the chopped walnuts.

Pour the batter into the prepared baking pan and smooth the top. Bake for 35-40 minutes or until a toothpick comes out clean.

Allow the cake to cool in the pan for about 10 minutes before inverting onto a wire rack to cool completely.

Make the cream cheese frosting by beating together the cream cheese and softened butter until smooth, then gradually add powdered sugar.

Once the cake is cool, spread the cream cheese frosting evenly across the top. Optionally garnish with additional chopped walnuts.