I prepare topping first. In a small bowl add sugar, room temperature butter, cinnamon and flour. I mix it with a spoon first not to create dust clouds (if you want to stay in dust cloud you can start mixing it with mixer right away), mix it well, then mix it on medium speed with hand mixer for 1 minute. Set aside.
In a bowl of electric mixer add egg, white sugar and brown sugar and mix it on high for 3 minutes.
Add buttermilk. Mix it on medium for 1 minute.
Add flour, salt and baking soda through the sifter. Mix it on low (stir) for 2 minutes or until all combined.
In a small bowl peel and mix bananas with a hand mixer for 1 minute. Add mixed bananas to the batter.
Wash, peel, slice then chop apple. I use onion chopper, it works great and fast. Add chopped apple to the batter.
Stir it on low until combined for about 1-2 minutes.
Preheat oven to 350 F. Pour about ½ cup of the batter into cupcake pan lined with foil cupcake cups. I like to use foil cupcake cups for this muffins, because it peels easy without getting stuck to the pan. I used paper cupcake holder and its gets stuck to the paper. I will try to make them in silicon cupcake cups in the future and see how it works. If you have them, use them and let me know if it comes out easy without sticking to the cup.
Add teaspoon of the cinnamon topping on top of each muffin. Bake it for 30 minutes at 350 F.
Remove from the oven and let them cool for 5 minutes before removing them from the pan. After it completely cools decorate with cream cheese frosting – optional.