Pre-heat your oven to 325 degrees. Grease a muffin pan or use muffin cups if you prefer.
In a bowl, mix together the cinnamon-sugar filling ingredients and set aside.
In a stand mixer (or by hand will work too), cream the bananas and sugar together. Then add in the 2 eggs and cinnamon and mix thoroughly.
In a separate bowl, sift together the flour, baking soda, baking powder and salt. Once you've got the dry ingredients properly sifted together, start adding them to the wet ingredient mixture a little at a time. Mix together well, scraping the sides of the bowl a time or two as needed.
Finally, add in the sour cream and vanilla to the batter and mix. Once the sour cream is completely combined into the batter, you're ready to start pouring into the muffin cups.
In the muffin pan (I used a silicone muffin pan) fill each cup halfway. Then you will carefully spoon on some of the cinnamon-sugar filling to coat the entire middle of the muffin. Then you will pour more batter into the muffin cups until each one is full. Finally, you will sprinkle the tops with more cinnamon-sugar filling so they look like the photo when they are ready to go into the oven.
NOTE: there will be plenty of cinnamon-sugar filling, so don't feel like you have to use it all.
Pop them in the oven for 22-25 minutes. Stick a toothpick in and if it comes out clean, then they are done!
Serving Size 1 muffin