Preheat the oven to 350°F. Smash the ripe bananas in a large mixing bowl. Mix in the melted butter until combined. Mix in the sugar, egg, vanilla, almond extract, and bourbon, then the spices. Sprinkle the baking soda and salt over the mixture and mix in. Add the flour and mix to combine.
Butter a 8"x8" pan. Lay overhanging parchment paper in the pan (this will help you to remove the cake later). Pour the batter into the pan and bake for 45 minutes. After baking, cool in pan.
Place the sweetened condensed milk can on its side in a large pot. Fill the pot with room-temperature water, making sure the water level is at least 2 inches above the can. Set pot over high heat and allow to come to a simmer. Reduce heat and simmer for 1 1/2 hours. Using a pair of tongs, remove the can from the water and set on a wire rack to cool to room temperature (DO NOT OPEN the can while it's hot).
Using an electric mixture with a wire whisk attachment, whip the softened butter on medium speed. Slowly add the confectioner's sugar and salt. Add the entire can of cooled dulce de leche.
frost the cooled cake heavily, and top with walnuts!