Preheat oven to 350F (176C). Butter and flour your pans very well.

In a mixing bowl, mix the butter and white sugar on high speed and cream it until light and fluffy, about 1-2 minutes. Add in the brown sugar and beat for another 30 seconds. Mix in the egg until well combined. Lower speed to medium and add in the sour cream, banana, vanilla and rum until well combined.

Sift together the flour, baking soda, baking powder and salt. Add it in small batches on low speed until JUST combined. Fold in the walnuts with a spatula and pour the batter into your bundt pan. Bake for 30 minutes or until a toothpick comes out clean. Allow the cake to cool for in the pan for at least 15 minutes before gently inverting it. Set aside.

Buttered Rum Glaze: add all the ingredients to a medium sauce pan and stir well. Bring to a boil and cook for 5 minutes. Remove from heat and let cool.

Remove the cake from pan. Then wipe the pan clean and put the cake back in it (I like to remove the cake first, to make sure to get it out easily). Poke holes all over the bottom of the cake and gently pour in the glaze 1/3 at a time waiting for it to soak all the way in before you pour the next part in. Reserve a little for topping. Allow the cake to soak up the glaze and then invert it onto a serving dish. Spoon remaining glaze on top. Serve alone or with dollops of ice cream. Enjoy!

Freezing Instructions: Bake the cake but do not make the glaze sauce. Allow cake to cool completely then wrap in plastic wrap then tinfoil and store in the freezer for up to 3 months. Thaw cake completely in refrigerator overnight. When ready to eat, make the sauce, poke holes in the cake and gently pour the glaze on top. Allow it to rest for at least 30 minutes before serving.