Preheat the oven to 350°F (175°C). Grease and sugar a 10-inch (25cm) bundt pan - 10-12 cups (2.4-2.88l) in size. Make sure the inside of the pan is completely and evenly coated, and no spot is left. Set aside.
In a medium bowl, combine the flour, baking soda, salt, and cinnamon and set aside.
In a large mixing bowl, using an electric mixer fitted with a whisk or paddle attachment, cream together the butter and sugar on medium speed until it is a fluffy, soft-crumbly texture, about 2-3 minutes. Add the eggs, one at a time, and mix until incorporated and smooth, about 1-2 minutes. Then add the mashed bananas, oil, and vanilla and mix until smooth and combined, about 1 minute. Alternately add the flour mixture and the sour cream, beginning and ending with the flour mixture, and stir just until combined. Fold the chocolate chips and chopped bananas into the batter until well distributed.
Pour the batter into the prepared bundt pan, spread evenly, and bake for about 55-70 minutes or until a toothpick inserted into the center comes out clean. Remove from the oven and let the cake cool in the pan for 10 minutes. Then invert the cake onto a wire rack or plate and let it rest for another 10 minutes if the cake doesn't come out right away. Then lightly tap on the pan to loosen the cake if necessary. Let cool completely.
Once cooled, serve as it is, or decorate to your liking. Store in an airtight container at room temperature for up to 4 days or freeze for up to 2 months.