Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a mixing bowl, combine flour, sugar, baking powder, baking soda, and salt.

In another bowl, cream together the softened butter and mashed bananas until smooth.

Add eggs and vanilla extract to the banana mixture and mix well.

Gradually add the dry ingredients to the wet ingredients, alternating with buttermilk, and mix until just combined.

Divide the batter evenly between the prepared cake pans.

Bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then transfer to wire racks to cool completely.

In a mixing bowl, beat the softened butter until creamy.

Gradually add powdered sugar and mix until well combined.

Add vanilla extract and milk, mixing until the frosting is smooth and spreadable.

Once the cakes are completely cool, place one layer on a serving plate.

Spread a layer of frosting on top of the first cake layer.

Place the second layer on top and frost the top and sides of the cake.

Decorate as desired and serve.