Preheat your oven to 350°F (175°C) and grease and flour two 9-inch round cake pans.

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

Stir in the mashed bananas, eggs, sour cream, and vanilla extract. Beat until combined.

In another bowl, sift together the flour, baking powder, baking soda, and salt.

Gradually add the dry mixture to the banana mixture. Stir until just combined.

Fold in the chopped walnuts gently.

Divide the batter evenly between the prepared cake pans.

Bake in your preheated oven for about 25-30 minutes or until a toothpick inserted in the center comes out clean.

Let the cakes cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.

While the cakes are cooling, beat the heavy cream with powdered sugar and vanilla extract in a chilled mixing bowl until soft peaks form.

Once the cakes are completely cool, place one layer on a serving plate and spread some frosting on top.

Place the second layer on top and frost the top and sides.

Decorate with extra walnuts or banana slices if desired.