Make the Cake:

1. Preheat & Prep: Preheat the oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan (or two 8-inch round cake pans).
2. Mix Dry Ingredients: In a medium bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon. Set aside.
3. Cream Butter & Sugar: In a large bowl, beat the butter, granulated sugar, and brown sugar until light and fluffy (about 2 minutes).
4. Add Eggs & Bananas: Beat in the eggs one at a time. Stir in vanilla extract, then fold in mashed bananas.
5. Combine & Add Walnuts: Alternately add the dry ingredients and buttermilk, mixing gently until just combined. Fold in the chopped walnuts.
6. Bake: Pour the batter into the prepared pan. Bake for 30-35 minutes (or until a toothpick inserted in the center comes out clean).
7. Cool: Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before frosting.

Make the Frosting (Optional):

1. Beat the cream cheese and butter together until smooth.
2. Gradually add powdered sugar and vanilla, beating until fluffy.
3. Spread evenly over the cooled cake.