Preheat oven to 425 degrees Fahrenheit.
In a medium bowl whisk dry ingredients together and set to the side.
In a large bowl, blend bananas and butter together. Add vanilla, brown sugar, egg, and milk. Mix well with a hand blender.
Gently pour dry ingredients into wet ingredients bowl. Mix with hand blender. DO NOT OVER MOnce mixed, add in walnuts, and gently fold it in.
For jumbo muffins, grease muffin tins and divide evenly over 6 muffin tins.
For cupcake sized muffins, grease or add liners into cupcake tin. Divide evenly over 10-12 cupcake openings.
Bake at 425 for five minutes, then lower temperature to 350 degrees for 16-18 minutes for jumbo muffins and 13-14 minutes for cupcake sized muffins.
Remove from heat and allow muffins to cool.