Preheat the oven to 425°F (218°C). Line a 12-cup muffin pan with liners or grease well.

In a bowl, mash the bananas with a fork until mostly smooth with no large lumps.

In another bowl, whisk together flour, baking soda, baking powder, cinnamon, and salt. Set aside.

In a mixing bowl, beat the butter until creamy, about 3 minutes. Add brown sugar and mix until light and fluffy, scraping down the sides as needed.

Add mashed bananas, eggs, buttermilk, and vanilla extract. Mix until combined.

Add the dry ingredients to the wet mixture and gently stir with a spatula until just combined. Do not overmix.

Fold in 1/2 cup of the chopped walnuts.

Divide the batter evenly among the muffin cups. Sprinkle the remaining walnuts on top.

Bake at 425°F (218°C) for 5 minutes, then reduce the oven temperature to 350°F (177°C) and continue baking for 15–17 minutes, or until a toothpick inserted in the center comes out clean.

Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Use very ripe bananas for best flavor and sweetness.

Do not overmix to keep muffins soft and tender.

The high initial baking temperature helps create a domed top.

Room Temperature: Store in an airtight container for up to 3 days.

Refrigerator: Store up to 1 week.

Freezer: Freeze for up to 3 months and thaw before serving.

Course: Breakfast / Snack

Cuisine: American