Preheat oven to 350 degrees F. Butter a 9- or 10-inch Bundt pan. Whisk together flour, baking soda, and salt; set aside. In the bowl of a standing mixer, beat butter and sugar on medium speed until fluffy, about 3 minutes. Beat in eggs one at a time, for about a minute after each, then mix in vanilla. Reduce mixer speed to low and mix in mashed bananas.

Turn the mixer on low, add half of the flour mixture, the sour cream, and the rest of the flour mixture, just until mixed through.

Bake 65 to 75 minutes, or until inserted cake tester comes out clean. Start to check the cake after 30 minutes, and if it is already a dark-gold color, cover the cake with a piece of tented foil to prevent burning.  Cool the cake in its pan on a cooling rack for 10 minutes, then unmold the cake onto the rack to finish cooling.

To make cream cheese frosting, mix butter and cream cheese in a mixer.  Add vanilla and powdered sugar and mix until smooth.  Let cake cool completely before frosting.

Store tightly wrapped in plastic.