In a medium bowl, add dry ingredients. Whisk together and set to the side.
In a large bowl, fold bananas, pumpkin, 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 MIX. Once mixed, add in nuts (optional) 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 for 18-20 minutes for jumbo muffins and 20-25 minutes for regular sized muffins