How to Make It
Preheat oven to 325°F. Grease a 9- x- 13-inch metal cake pan with cooking spray and line the bottom with parchment paper; set aside.
Make Cake: In a bowl, whisk together flour, cornstarch, baking powder, baking soda, salt, cinnamon, and ginger; set aside. In a separate bowl, mash bananas until liquid and homogenous. Add eggs and vanilla to bananas, and mix until well combined; set aside. In a stand mixer, cream together butter and sugars until light and fluffy, about3 minutes. Scrape down sides of bowl, add banana mixture and mix until combined (the mixture will look split and that’s perfectly fine). Using a spatula, mix the dry ingredients into the batter by hand until no pockets of dry ingredients remain. Fold in 1 cup walnuts.
Spread batter evenly in prepared pan and bake until a toothpick inserted in the center comes out clean, 45 to 50 minutes. Allow to cool completely before inverting on a cutting board, removing parchment paper, and gently flipping over so the top of the cake is facing up.
Make Frosting: While cake cools, cream together butter, cream cheese, and salt untilwell combined and fluffy, about 3 minutes. Add vanilla and mix on low until combined. Add half of the powdered sugar and mix on low until combined. Add remaining powdered sugar and mix on low until incorporated, increase speed to high and beat for 5 minutes.
Spread the frosting evenly over the cake, using a spatula or spoon to make decorative swooshes. Use remaining walnuts to line theperimeter of the cake.