Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or line it with parchment paper.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, beat the room temperature butter and granulated sugar together on medium speed until light and fluffy, about 3-4 minutes.

Add the eggs, one at a time, mixing well after each addition. Stir in the mashed bananas and vanilla extract until well combined.

Gradually add the dry ingredients into the banana mixture, alternating with buttermilk. Begin and end with the dry ingredients. Mix until just combined.

Carefully fold in the chopped walnuts using a spatula until they are evenly distributed throughout the batter.

Pour the batter into the prepared cake pan and smooth the top. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Allow the cake to cool in the pan for 10 minutes before turning it out onto a wire rack. Let it cool completely before frosting.

In a medium bowl, beat the cold heavy cream, powdered sugar, and vanilla until stiff peaks form.

In another bowl, whip the softened cream cheese until smooth. Gently fold the whipped cream into the cream cheese until fully combined.

Once the cake is cooled, spread the cream mixture generously on top. Decorate with additional walnut pieces if desired.