Preheat oven to 350 degrees. In a mixing bowl whisk together flour, baking powder, baking soda and salt for 20 seconds, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment whip butter until slightly pale and fluffy. Add sugar and mix until pale and fluffy. Mix in eggs one at a time, adding in vanilla with second egg. Blend in mashed banana. Mix in half of the flour mixture, then mix in sour cream. Stir in remaining 1/2 of the flour mixture just until combined. Scrape down sides and bottom of bowl to ensure batter is properly combined.
Spray a 10 to 12-cup bundt pan with non-stick spray then dust with flour, shaking out excess. Pour batter into bundt pan, spread into an even layer. Bake in preheated oven until toothpick inserted near center comes out clean, about 40 - 55 minutes (12 cup pan will be more near lesser time). Cool in pan 5 minutes then invert onto a wire rack to cool completely. Once cool spread icing over top and sprinkle with chopped pecans. Store in an airtight container.
Make the icing:
In the bowl of an electric stand mixer fitted with the paddle attachment, whip together cream cheese, powdered sugar, vanilla and cinnamon. Add in enough milk, 1 tsp at a time, to reach desired consistency.
Notes
If you use salted butter in this recipe, omit the additional salt in the cake batter.