Preheat oven to 350°F.
Melt 1/2 stick butter in a large, heavy-bottomed skillet over medium-high heat, Add 1/4 cup of dark brown sugar and swirl to combine. Add the bananas and cook about 3 minutes. Add the banana liqueur and simmer for another three minutes. Remove the bananas and their sauce to a bowl and add 1/4 cup of the rum. Mash together with a fork or potato masher; set aside.
In a mixing bowl, whisk together the flour, baking soda, salt and spices.
In a stand mixer fitted with the paddle attachment, cream together remaining 1 stick butter and remaining 3/4 cup sugar for 3-5 minutes at medium speed, or until light in color and fluffy. Add in eggs one at a time until mixture is fully combined. Add in vanilla, sour cream and the cooled banana mixture. Turn down to low speed and add the flour mixture in batches.
Spray a 9x5 loaf pan with cooking spray. Pour the batter into a 9x5 loaf pan and bake for 1 hour or until a toothpick comes out clean.
While the bread is still hot, pour the remaining 1/2 cup rum over the top of the bread. Remove to a cooling rack and let cool.
Meanwhile, whip together the heavy cream, powdered sugar and rum in a large bowl or the bowl of a stand mixer. Serve slices of banana bread topped with the whipped cream.