This cake was made by Spice House staffer Bridget Petritis for a Retail Therapy night. It's adapted from a recipe in the March 2008 issue of Bon Appetit.
For Caramel-Walnut Topping:
Spray a 13x9 baking pan with nonstick spray.
Put butter, sugar, and corn syrup in a medium sauce pan, and scrape in 1 vanilla bean. Bring to a boil in a medium saucepan, stirring constantly. Boil for 1 minute after butter has completely melted. Stir in nuts and spread topping into prepared pan. Let topping cool.
Preheat oven to 350. Beat butter and both sugars in a large bowl until smooth. Scrape in second vanilla bean and stir until vanilla seeds are throughly mixed in. Be careful not to leave clumps, especially when using Tahitian beans. Beat in eggs, then add bananas, sour cream, rum, and vanilla.
Sift together flour, baking powder, baking soda, and salt in a medium bowl. Gradually beat dry ingredients into wet ingredients. Spoon batter over cooled topping. Bake at 350 for about 40 minutes, or until tester inserted comes out clean. Cool at least fifteen minutes.
Run a knife around the edges of the cake to loosen it from the pan. Place a platter over the pan, and flip cake onto platter so caramel is now on top of cake. Let stand five minutes before removing pan from cake.. Cool at least fifteen minutes so topping has time to set.