For the cake: Preheat the oven to 350 degrees F. Grease and flour two 8-inch round cake pans.
Cream the granulated sugar and butter with an electric mixer until light and fluffy. Mix in the vanilla, eggs and bananas. In a separate bowl, mix the flour, baking soda and salt. Mix the flour mixture into the butter mixture, alternating with the sour cream--do not overmix. Pour the batter into the prepared cake pans and bake until a tester comes out clean, 20 to 25 minutes. Let the cakes cool before removing from the pans.
For the buttercream: In a stand mixer with the paddle attachment, mix the salt, confectioners' sugar, vanilla and egg whites for 5 minutes on medium-high speed. Add the butter, little by little, and mix for 10 minutes. Fold in the chopped strawberries.
To assemble the cake: Using a serrated knife, cut the top dome off of the cakes to make them level. Cut one of the cakes in half horizontally to form 2 layers. Repeat with the second cake for 4 layers total. Place one cake layer on a serving plate and spread buttercream on top. Stack a second layer on top and spread buttercream on top. Repeat with the remaining 2 layers. Using an offset spatula, spread buttercream on the outside of the cake. Smooth using up and down strokes, and then scrape off any excess buttercream.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.