Preheat the oven to 350F degrees.
Grease and flour a 12-cup bundt pan.** Be sure that all the creases and indentations are well covered.
In a medium bowl whisk together the flour, baking soda, cinnamon and salt.
In a large bowl beat the butter, white sugar and brown sugar until fluffy.
Beat in the eggs and vanilla extract.
Mix in the mashed bananas.
With the mixer on low speed, mix in about ½ of the flour mixture. Then mix in the sour cream.
Turn off the mixer and scrape down the sides of the bowl.
Then mix in the rest of the flour mixture, followed by the milk. *The batter will be thick.
Spoon the batter into the prepared bundt pan and smooth the top.
Bake in the preheated oven for 55-65 minutes, or until an inserted toothpick comes out clean or the top feels slightly springy to the touch.
Cool for 15-30 minutes, then gently insert the bundt pan onto a plate to release the cake. Do not insert the cake immediately, or it will be too hot. Waiting too long to insert the cake can make it more difficult to get out of the pan.