Preheat oven to 350 degrees Grease a 9x13 inch metal baking pan.
Cream together butter and sugar with an electric mixer or stand mixer fitted with the paddle attachment. Beat in the yogurt (or sour cream) and eggs and until thoroughly combined. Mix in the bashed bananas and vanilla extract.
Add the flour, baking soda, and salt and mix well. Pour into prepared baking pan and spread evenly. Bake for 33-35 minutes until toothpick comes out clean when inserted in the middle of the cake.
Let cake cool completely before adding frosting.
For the Frosting:
Beat butter and cream cheese together until smooth. Add the vanilla and powdered sugar and mix until thick and spreadable. Spread over the top of cooled cake.