Preheat your oven to 350°F (175°C). Grease two 8-inch cake pans and set aside.
In a large mixing bowl, combine the flour and sugar. Mix briefly to aerate the dry ingredients.
Add the melted butter, mashed bananas, eggs, and vanilla extract to the dry mixture. Beat with an electric mixer or whisk until the batter is smooth and slightly thickened, about 2-3 minutes.
Fold in the toasted walnuts gently to evenly distribute throughout the batter.
Divide the batter evenly between the prepared cake pans, smoothing the tops with a spatula.
Bake the cakes for 35-40 minutes, or until a toothpick inserted into the center comes out clean. The cakes will be golden and fragrant.
Remove the cakes from the oven and let them cool in their pans for 10 minutes. Then, transfer to a cooling rack and cool completely before assembling.
While the cakes cool, whip the heavy cream with powdered sugar until soft peaks form. It should be light, fluffy, and slightly sweet.
Once the cakes are cooled, spread a generous layer of whipped vanilla cream over the first cake layer.
Place the second cake layer on top and gently press down to set, then cover the top with remaining cream. Decorate with extra chopped walnuts if desired.
Slice and serve the cake once the cream has settled. Enjoy the moist cake with crunchy walnuts and smooth vanilla filling.