Preheat oven to 400°F degrees. Lightly grease a 12-cup muffin tin or line with cupcake liners. Set aside.
In a large bowl, whisk together the flour, baking soda, pumpkin spice seasoning, and salt. Set aside.
In the bowl of a stand mixer or in a large bowl using a hand mixer, mix together the mashed banana, pumpkin puree, and sugar until smooth.
Beat in the melted butter, then one egg at a time, and finally the vanilla. Mix until the ingredients are just incorporated.
Gradually mix in the dry ingredients, just until incorporated and you don’t see anymore dry flour mix.
Use a ¼ cup measuring cup to scoop the batter and divide evenly between muffin tins, filling each about ¾ of the way full.
Bake at 400°F for 5 minutes, then turn down the heat to 350°F and bake for an additional for 15 to 20 minutes, or until a toothpick comes out clean from the center of the muffins.
Allow muffins to cool in the muffin tin for 5 minutes, then transfer to a wire cooling rack.
Notes
Spices: If you don't have pumpkin pie spice, you can use a mix of ¼ tsp cinnamon, ¼ teaspoon nutmeg, ¼ teaspoon ground ginger, and ¼ teaspoon all spice. Feel free to also add ¼ teaspoon of clove if you want, and/or use just a little bit (⅛ - ¼ tsp) more cinnamon. Storage: store muffins in an airtight container at room temperature for up to four or five days.Heat: Baking the muffins at a higher heat for 5 minutes, then lowering the heat for the remainder of the baking time helps create the classic risen muffin dome on top. You can bake it at 350°F for the entire 20-25 minutes instead if you don't care for the muffin dome, or if you just prefer to bake it at an even temperature the entire time.