Preheat your oven to 350°F and line a 12-cup muffin pan with paper liners. While the oven heats, measure out all your dry ingredients—flour, baking soda, baking powder, salt, and cinnamon—into a small bowl and whisk them together to distribute the leavening agents evenly. Chop your walnuts into roughly 1/4-inch pieces and set aside. This prep work ensures everything is ready when you need it, preventing overmixing of the batter later.

In a large mixing bowl, mash the very ripe bananas until mostly smooth with just a few small lumps remaining—this texture keeps the muffins moist and tender. Add the softened butter to the warm bananas and stir until well combined and creamy. Mix in the packed brown sugar, then add the eggs one at a time, stirring well after each addition. Finish by adding the vanilla extract and mix until everything is fully incorporated. I like to use very ripe bananas with plenty of brown spots because they provide natural sweetness and moisture, reducing the need for additional sugar.

Pour the wet mixture from Step 2 into the bowl with your dry ingredient mixture from Step 1. Using a spatula or wooden spoon, fold the ingredients together with just 15-20 gentle strokes until the flour is barely incorporated—you should still see a few streaks of flour. Stop mixing immediately once no dry flour is visible; overmixing develops gluten and creates tough, dense muffins. Gently fold in the chopped walnuts from Step 1 until evenly distributed.

Divide the batter evenly among the 12 lined muffin cups, filling each about two-thirds to three-quarters full. Place the pan in your preheated 350°F oven and bake for 20-22 minutes, until a toothpick inserted into the center of a muffin comes out with just a few moist crumbs—not completely dry. The muffins are done when the tops are golden brown and spring back slightly when lightly touched. I always insert the toothpick in the center muffin first, as it takes longest to bake.

Remove the muffin pan from the oven and let it cool in the pan for 5 minutes—this allows the muffins to set without becoming dry. Gently turn the muffins out onto a wire rack to cool further, or serve them warm directly from the pan with a pat of butter if desired. These muffins are best enjoyed fresh but will keep in an airtight container for up to 3 days.