Preheat oven to 350 degrees, and grease six 9-inch cake pans with vegetable oil spray.
In a large bowl, combine cake flour, 2 cups of sugar, baking powder and soda, salt, oil, bananas, 2 teaspoons vanilla, egg yolks and buttermilk.
In a separate bowl, beat egg whites, 1/2 cup sugar, 2 teaspoons vanilla and cream of tartar with a hand mixer until stiff peaks form. Fold meringue mixture into banana mixture to combine. Pour into pans and bake until light golden brown and a toothpick inserted in the center comes out clean, roughly 20 to 25 minutes. Cool for 10 minutes, then unmold onto a rack to cool completely before frosting.
Make the icing:
In the bowl of a stand mixer with the paddle attachment, cream butter and cream cheese until smooth. Add powdered sugar, lemon juice and vanilla. Mix until combined.
Assemble the cake:
Place a layer on a cake plate and cover the top with a half cup of frosting. Spread to create an even layer, approximately a half-inch thick. Continue until all layers are used and you have a towering six-layer cake. Finish the top layer with the remaining frosting. Cake will keep up to 5 days covered at room temperature.