Melt butter and chocolate for 1 minute over medium heat and stir until it is completely melted.
Stir in sugar, egg, vanilla into the chocolate mixture. Add flour and salt and mix until smooth.
Set aside to cool completely
Prepare a 9-x-5-inch metal loaf pan with baking spray then set aside.
Using a stand mixer with a paddle attachment, beat butter and sugar until light and fluffy for about 3 to 4 minutes on medium.
Add eggs one at a time and beat. Then add vanilla extract, bananas and buttermilk.
Sift flour, baking powder, baking soda and salt and fold it using a rubber spatula until the banana batter is smooth.
Scoop half of the banana batter into the prepared loaf pan and spread evenly then spread the brownie batter over the banana batter and then add the remaining banana batter.Bake for about 45 to 55 minutes until a toothpick inserted in the center comes out clean
Transfer to a wire rack and let cool for 10 minutes then remove and let the cake cool on a cooling rack.
Cut into slices and serve with any toppings of choice
Banana made with banana giving it a very authentic taste.