Preheat oven to 350°F. Be sure to adjust the oven rack to the lower-middle position.
Grease the pan: Grease a 8.5 x 4.5 inch light colored loaf pan with softened butter. Evenly spread a thin layer of butter over the interior surface of the loaf pan. Be sure to cover the bottom and sides, including the corners. Add a tablespoon or two of all-purpose flour to the pan. Tilt and rotate the pan, tapping it gently, to distribute the flour evenly across the greased surface. The flour will stick to the butter, creating a light, floury coating. Hold the greased and floured pan upside down over the sink or a trash can to allow any excess flour to fall out. Gently tap the pan to help remove loose flour.
In a medium skillet add the mashed bananas, butter, brown sugar, and rum. Cook and whisk banana mixture over medium heat until butter melts and mixture begins to simmer. Turn the heat down to low and let simmer for ~3-5 minutes, whisking occasionally.
3 large over ripe bananas, mashed (~1 1/4 cups), 1/2 cup brown sugar, packed, 1/2 cup unsalted butter (plus 1 Tbsp. for greasing the loaf pan), 3 Tbsp. Dark Rum or Spiced Rum
Remove from heat and let slightly cool for about 10 minutes. It does not have to cool all the way, but just so it is not super hot. (If you are folding in chocolate chips into the batter you will want it to cool completely).
In a large bowl, combine the eggs, oil, sour cream, buttermilk, and vanilla extract.
2 large eggs, room temperature, 1/4 cup vegetable oil, 1/4 cup buttermilk, room temperature, 1 tsp. vanilla extract, 1/4 cup sour cream, room temperature
Add the cooled banana mixture to this and whisk together.
In a separate mixing bowl, combine the flour, sugar, baking soda, salt, nutmeg, cinnamon, and cardamom.
2 cups flour, spooned and leveled, 2/3 cup granulated sugar, 1 tsp. baking soda, 1/2 tsp. salt, 1 tsp. ground nutmeg, 1/4 tsp. cinnamon, 1/4 tsp. cardamom
Add the dry ingredients to the wet ingredients and gently fold until combined. Do not over mix the batter.
Pour this mixture into the prepared pan.
Bake for ~60-65 minutes, or until a toothpick comes out clean.
While the bread cools, you can prepare the frosting. Whisk powdered sugar, rum and butter together. Add more or less powdered sugar and rum until you get the desired frosting consistency; either drippy for a glaze or more thick like a frosting in the photos.
1-2 cups powdered sugar, 1-2 Tbsp. rum, 2 Tbsp. unsalted butter, melted
Make sure your bread is 100% cooled down before you drizzle the frosting over the bread. Enjoy!