Preheat oven to 350°F. Generously grease a 10-12 cup bundt pan with butter and then dust with flour. Set aside.
Whisk together the flour, baking powder, baking soda and salt in a small bowl. In a large mixing bowl, beat the butter and the sugar with an electric mixer until light and fluffy.
Add the eggs and vanilla and beat again. Stir in the banana, and then add half of the dry ingredients. Stir until combined. Add the sour cream, stir, and add the remaining dry ingredients. Stir until combined and then stir in 1/2 cup chopped pecans.
Pour the batter into the pan and spread evenly. Bake about 40-45 minutes, until toothpick inserted comes out mostly clean or with crumbs. Cool 5 minutes in pan and then invert on wire rack to cool completely.
To make the icing, combine the cream cheese, powdered sugar, vanilla, and cinnamon in a large mixing bowl. Beat until fluffy, adding a tablespoon of milk and then an additional teaspoon at a time to reach the desired consistency.
Spoon the icing over the completely cooled cake and sprinkle with remaining pecans. Serve immediately or refrigerate until ready to serve. Store covered in the refrigerator for 3-4 days. Enjoy!