Grease muffin pans or line with paper liners. Set aside.
In a medium bowl, combine dry ingredients (flour, baking powder, baking soda, cinnamon, and salt). Set aside.
In the bowl of a food processor, pulse butterscotch chips until chopped medium-fine. I pulse them until they're about the size of mini chocolate chips. Set aside.
In the bowl of a stand mixer, combine the butter and sugar. Beat until light and fluffy. Scrape down the sides of the bowl.
Add egg, then scrape down the sides of the bowl again. Add buttermilk (see note), vanilla, and mashed bananas and mix to combine.
With the mixer running on low speed, gradually add the dry ingredients. Mix just until combined. Fold the butterscotch chips into the batter with a spatula.
Fill each the wells of the muffin tin about ¾ full and chill for at least an hour (up to overnight). This step to chill the batter will result in taller, rounder muffins, but it is optional if you're short on time!
Preheat oven to 425° F. Sprinkle the tops of the muffins with raw sugar, if desired.
Bake 7 minutes at 425°F, then *without opening the oven door*, reduce the heat to 350° F and bake for an additional 10-15 minutes, or until a toothpick inserted in the center comes out clean. Total bake time will depend on the size and moisture content of the bananas you're using, so start checking them at 10 minutes to see if they're done!
Cool muffins in the pans 10 minutes, then remove to a wire rack to cool.
Store baked and cooled muffins in an airtight container on your counter for up to four days. Placing some paper towel in the bottom of the container before you add the muffins will help to absorb any excess moisture and keep them good longer.Muffins can be frozen in an airtight container for up to three months.Enjoy!
Notes
Note on buttermilk: If you don't have it on-hand, you can do a quick substitution with vinegar or lemon juice and milk (2% milkfat or higher). Just put 1 ½ teaspoons of vinegar or lemon juice in a liquid measuring cup, then pour in the milk to the ⅔ cup line. Stir, let sit 5 minutes, and then it's ready for use!Note on butterscotch chips: If you can't find them in your local grocery store, you can get them here! Of course, you can substitute with chocolate chips if you'd like.