1. Prepare a 9×13 pan with baking spray. Preheat oven to 350°F (176°C).
2. In a large mixing bowl, cream the butter and sugar together until light in color and fluffy, about 3-4 minutes. Do not skimp on the creaming time.
3. Add sour cream and vanilla extract and mix until well combined.
4. Add egg whites in two batches, mixing until well combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Combine dry ingredients in a separate bowl, then combine the milk and water in a small measuring cup.
6. Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
7. Pour the batter into the prepared cake pan and bake for 28-30 minutes.
8. While the cake bakes, make the banana pudding. Add the egg yolks to a medium bowl, whisk together and set aside.
9. In a large saucepan, combine the sugar and cornstarch, then add the milk. Cook over medium heat until it gets warm, about 5 minutes.
10. Add some of the milk mixture to the egg yolks and whisk together to temper the eggs. Add the egg mixture back into the saucepan.
11. Continue cooking the milk mixture over medium heat and slowly bring to a bowl, about 10 minutes.
12. Allow the mixture to boil for 5 minutes, stirring continuously, then remove from the heat and add the butter and extracts.
13. When the cake comes out of the oven, use the end of a wooden spoon or something similar to poke good sized holes all over the cake.
14. Pour to pudding over the cake and allow it to settle into the holes. You’ll have some pudding settle on top of the cake as well.
15. Place the cake into the fridge to cool and firm, 2-3 hours.
16. When the cake has cooled, make the whipped cream. Add the cream, powdered sugar and vanilla extract to a large mixer bowl and whip on high speed until stiff peaks form.
17. Place sliced bananas in an even layer over the top of the cake and pudding.
18. Spread the whipped cream evenly over the bananas, then top of the cake with the crushed vanilla wafers.
19. Refrigerate cake until ready to serve. Cake is best served cool, but not cold. Cake will last well covered in the fridge for 3-4 days.