Preheat the oven to 350˚F and line a 24-cup mini muffin tins with parchment paper liners.
In a medium bowl, whisk together flour, baking soda, cinnamon and salt.
In a separate large bowl, add banana and mash until smooth. Add brown sugar and whisk until smooth, about 2 minutes. Add butter, yogurt, egg, and vanilla extract and whisk until combined, about 1 minute more.
Add the dry ingredients to the wet ingredients, folding them with a rubber spatula just until no streaks of flour remain.
Fill each muffin cavity with a heaping tablespoon of batter (it should come to the top of the tin). Bake for about 14 to 16 minutes, or until a cake tester inserted in the center of a muffin comes out clean.
Notes
Storage: These mini banana muffins can be kept in an airtight container (or bag) in the fridge for up to a week. You can also freeze them for up to 6 months. I recommend stashing them in a zipper-lock freezer bag to prevent freezer burn.