Heat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans, or line them with parchment paper for easy removal.
In a medium bowl, whisk together flour, baking soda, and salt. This ensures the leavening is evenly distributed.
In a large bowl, beat the softened butter and sugar until light, fluffy, and pale — about 3 minutes. This step traps air for a softer cake.
Beat in the eggs one at a time, then stir in vanilla extract. Make sure everything is well incorporated.
Mix in mashed bananas and sour cream. The batter should look creamy and slightly thick.
Gradually add the dry mixture into the wet ingredients, stirring gently until just combined. Avoid overmixing to keep the cake tender.
Use a spatula to fold in chopped walnuts and white chocolate chips for extra flavor and texture.
Divide the batter evenly between prepared pans. Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.
Let the cakes rest in the pans for 10 minutes, then transfer to wire racks to cool completely before layering.
Place one cake layer on a serving plate. Spread with 1 cup custard. Top with the second cake layer and spread remaining custard on top.
Decorate with banana slices and walnuts. Refrigerate at least 1 hour before serving for neat, firm slices.
