- Make caramel rum sauce and crumb topping, cover and set aside. Each can be made up to 2 weeks earlier, stored in the refrigerator. (You can also make the caramel rum sauce while the cake is baking.)
- Preheat oven to 350 degrees and grease an 8×8 inch square pan.
- Using an electric mixer, beat the butter, sugars, egg and egg whites on high speed until light and fluffy, about 5 min. If you’re using a standing mixer, use the whisk attachment.
- Chop the bananas into chunks and add to the butter-sugar-egg mixture. If you’re using a hand held mixer, mash the bananas into the batter a bit with the beaters before turning the mixer on. If using a standing mixer, switch to the paddle attachment. Beat the bananas into the batter until well incorporated. You will still have small pea-size chunks, which is ok.
- In a medium size bowl mix the flour, baking soda and salt with a wire whisk until combined.
- Mix the vanilla and milk in a measuring cup.
- Add the flour mixture and vanilla-milk mixture to the banana batter in alternating additions, starting and ending with the flour (1/3 of the flour mixture, 1/2 of the milk, 1/3 of the flour mixture, rest of the milk, rest of the flour mixture). After each addition beat the batter on medium speed just long enough to incorporate, scrapping down the sides of the bowl with a spatula as necessary. Don’t over mix.
- Pour the batter into your prepared pan. Top with 3 cups of crumb topping. The trick to getting large crumbs is to squeeze the topping together in your hand as you place it on the cake batter.
- Bake for 60-65 minutes, until the center isn’t jiggly and a toothpick inserted in the center comes out mostly clean. Let cool on a wire rack about 20 minutes, until still warm but not hot.
- Drizzle 1/4 – 1/2 cup of the caramel rum sauce over the top of the cake. With a knife, gently poke holes all over the cake, encouraging some caramel rum sauce to seep into the holes. Use the knife to cover each small hole with sauce. With the knife, gently press the sides of the cake away from the pan and allow some sauce to drizzle down the sides.
- Serve with additional caramel rum sauce, warmed slightly, for those people (like me) who think you can never have too much.