Preheat oven to 350 degrees F and grease a nine inch round pan then coat evenly with flour. Set aside.

In a large bowl, add together milk, mashed bananas, oil, both sugars and eggs. Mix until all ingredients are well combined.

Slowly add flour and mix until a thick and smooth batter forms.

Pour the batter into prepared pan and bake for about 40 minutes or until a toothpick comes out clean once inserted in the center.

Allow the cake to cool completely.

As the cake cools, prepare the buttercream frosting. In a large bowl, add butter, confectioner's sugar and milk. Use an electric mixer to beat until a smooth frosting forms. You will want this frosting to be a bit looser than cupcake frosting. However, if you find it too runny, add confectioner's sugar one tablespoon at a time.

Once the cake is cooled, use a spatula to frost the cake. Garnish with brown sugar.