MAKE THE CAKE:
- In a mixer combine sugar, oil, egg, milk, vanilla, and bananas cut up into small pieces. Mix on low for 1 minute.
- Add in flour, salt, baking powder, baking soda, cinnamon, and nutmeg. Mix on medium for 2 minutes.
- Set aside.
MAKE THE TOPPING:
- Put the butter in the bottom of a glass 8x8 Pyrex baking dish and melt it in the microwave for 30 seconds. You can use a round 9 inch pan as well and melt the butter in a separate microwave safe container.
- Add the vanilla and rum. Stir well.
- Add the brown sugar and stir until completely combined.
- Top with walnuts to cover baking dish evenly.
- Pour batter over the top and spread out evenly.
- Bake at 350 for 45-50 minutes or until fork comes out clean.
Let cake cool for 5 minutes or so. Then use a butter knife to separate the sides of the cake from the baking dish. Place a plate on top of the baking dish, hold tightly with both hands, and invert quickly onto the serving plate.