Cream together butter and sugar. Add the sour cream.
Add the mashed banana, egg, and vanilla.
Add the flour, salt, and baking soda. Stop mixing as soon as it is combined.
Pour the batter into a 9×9 pan that has been coated with cooking spray.
Bake in a preheated 375 degree oven for 20 to 25 minutes. The cake will be done when a tester comes out clean.
Let the cake cool completely. Start on the frosting by creaming together the butter and confectioners sugar. Add the heavy cream slowly and beat until smooth and fluffy. Add the scraped vanilla bean and a pinch of salt.
Spread the vanilla bean frosting over the cooled cake.