Step 1: Prepare the Cake Batter

1. Preheat your oven to 350°F (175°C). Grease two 9-inch cake pans and line them with parchment paper.
2. In a bowl, whisk together flour, baking soda, and salt. Set aside.
3. In a large mixing bowl, beat the butter, granulated sugar, and brown sugar until light and fluffy.
4. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
5. Mix in the mashed bananas until well combined.
6. Gradually add the dry ingredients, alternating with buttermilk, mixing until just combined.
7. Fold in the chopped walnuts gently.

Step 2: Bake the Cake

1. Divide the batter evenly between the prepared cake pans.
2. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
3. Allow the cakes to cool in the pans for 10 minutes, then transfer them to a cooling rack.

Step 3: Make the Cream Frosting

1. In a chilled bowl, beat the heavy whipping cream, powdered sugar, and vanilla extract until stiff peaks form.
2. Keep the frosting refrigerated until ready to use.

Step 4: Assemble and Decorate

1. Once the cakes are completely cool, spread half of the cream frosting over the first layer.
2. Place the second cake layer on top and spread the remaining frosting evenly.
3. Sprinkle the top with finely chopped walnuts for extra crunch and decoration.