Prepare a 12-cup muffin tin by filling each cup with a paper liner. If not using liners, grease each cup.

Preheat oven to 350°F.

In a large bowl, using electric hand mixer, beat the room-temperature butter and the sugar on high speed for about one minute. The ingredients should be well-combined but the mixture will appear to be coarse.

Add the eggs to the butter-sugar mixture. Continue beating for another minute until the mixture is creamy and smooth.

Add the mashed bananas, sour cream, pumpkin puree and vanilla extract to the mix and continue beating with the electric mixer until well combined, for about one more minute.

In a separate medium bowl, combine the flour, baking powder, baking soda and cinnamon. Mix with a whisk until well combined.

Add the dry ingredients to the batter and mix with a large spoon until just combined. Do not over-mix. There may be a few lumps, which will resolve during the baking process. Gently fold in 2/3 cup of the chocolate chips.

Divide the batter among the 12 muffin cups filling each to the top. Place five or six chocolate chips on the top of each muffin so that they will be visible after baking.

Bake for about 30 minutes. Check for doneness by inserting a wooden toothpick in the center of a muffin. If it comes out clean, they're done. Place tray on cooling rack.

When cool enough to handle, remove the muffins from the tin and allow them to cool a while longer on the rack until the chocolate has reset.