Preheat oven to 375 F. Line a muffin tin with muffin liners.
In a medium bowl, add flour, baking powder, baking soda, cinnamon, and salt. Whisk to combine.
In the bowl of a stand mixer, add the bananas. Using a fork, mash well.
Add sour cream, coconut oil, sugar, and egg to the bowl with the bananas. Place in stand mixer and mix with the paddle attachment until well combined.
Add dry ingredients and mix until well combined.
If using optional add ins (chocolate chips or chopped walnuts), stir them in with a wooden spoon.
Using a cookie scoop, scoop batter into muffin tin liners.
Bake for 15 to 18 minutes, or until tops of muffins are slightly golden brown. Test for doneness with a toothpick; if the toothpick comes out clean, the muffins are ready.