Preheat the oven to 325 degrees.
Grease and flour a large bundt pan.
Combine the flour, sugars, baking powder, baking soda, salt and cinnamon in a mixing bowl. Whisk and set aside.
In another bowl, combine the sour cream, milk, mashed bananas, vanilla and eggs. Mix well with a whisk.
Now cut your slightly cooler than room temperature butter into chunks. Turn your mixer on low and add in the butter slowly to your dry ingredients. Mix on medium to medium-high until all the flour is coated with the butter and the mixture is crumbly with a sand-like texture.
Pour in about a third of the liquid mixture. Mix on medium speed until combined. Only about 30 seconds.
Pour the last of the liquid mixture and mix on medium again until combined. Don’t overmix the batter. Only mix until everything is combined.
Use a rubber spatula and scrape the sides of the bowl. Mix again for only about 10 to 15 seconds.
Add in the mini chocolate chips and stir in by hand.
Pour into prepared pan.
Bake approximately 60-65 minutes. A toothpick inserted into the cake will come out with a few moist crumbs on it and not batter.
Set on a wire rack to cool for 15 minutes, then turn out onto the rack and let cool out of the pan completely.