Preheat the oven to 325 degrees F. Spray a quarter sheet baking pan with nonstick spray, line it with parchment paper, and spray again. Set aside.

In a medium mixing bowl, whisk together cake flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer with the paddle attachment, beat the butter and sugar on medium-high until light in color and fluffy, about 3 minutes.

Add the egg whites one at a time, scraping down the sides of the bowl between additions. Beat on medium-high speed for about 2 minutes. Add vanilla extract and stir to combine.

With the mixer on low speed, add 1/3 of the dry ingredients, followed by half of the buttermilk. Repeat with the remaining dry and wet ingredients. Mix until combined.

Scrape the sides and bottom of the bowl, mix for another 20 to 30 seconds, and gently fold in the sour cream.

Pour the batter into the prepared pan and bake for 18 to 20 minutes. Let cool in the pan for 15 minutes, then invert onto cooling racks to cool completely.

In a medium bowl, combine pudding mix, sweetened condensed milk, and milk. Mix until well blended. Transfer to a shallow dish, cover, and refrigerate until set, at least 2 hours.

In the bowl of a stand mixer with the whisk attachment, whip heavy whipping cream until medium-stiff peaks form. Fold into the pudding mixture. Cover and refrigerate until ready to build the cake.

In a small saucepan, mix sugar, water, and corn syrup over medium heat.

Heat heavy cream in a microwave-safe bowl for about a minute.

Bring the sugar mixture to a boil without stirring until it turns amber. Remove from heat and slowly stir in the cream to temper. Add salt and vanilla, then set aside to cool.

Preheat the oven to 375 degrees F. Line a baking sheet with parchment paper.

In a medium bowl, combine graham cracker crumbs, melted butter, sugar, and salt. Stir until damp. Spread on the baking sheet.

Bake for 8-10 minutes until golden brown. Let cool.

For assembly, put parchment on the counter. Invert the cake and peel off the bottom parchment.

Use a 6-inch cake ring to cut 2 circles and two half circles from the cake. The full circles are for the top layers, and the half circles and scraps form the bottom layer.

Clean the cake ring and line it with acetate. Place the half circles against the edge and fill the gap with scraps. Spread one-third of the banana cream pudding over the cake.

If using, spread sliced bananas over the pudding. Sprinkle 1/2 cup graham cracker crumbs and drizzle with salted caramel. Spread 1/2 cup whipping cream on top.

Insert a strip of acetate paper between the cake ring and the top of the first acetate strip. Set a cake round on top and repeat layers.

Cover the final cake layer with remaining banana cream pudding, graham cracker crumbs, caramel, and whipped cream.

Freeze for at least 12 hours. About 4-5 hours before serving, transfer to the refrigerator to thaw. Serve chilled.