Preheat oven to 400 degrees F. In a mixing bowl, whisk together gluten-free flour blend, baking powder, baking soda, xanthan gum, salt, and cinnamon for 20 seconds, set aside.
In a separate large mixing bowl, using an electric hand mixer set on medium speed (or in the bowl of a stand mixer fitted with paddle attachment), whip together butter, brown sugar and granulated sugar until creamy and fluffy.
Mix in eggs on a time, mixing until combined after each addition. Working in three separate batches, beginning and ending with flour mixture, add 1/3 of the flour mixture alternating with 1/2 of the mashed bananas and mixing until well blended after each addition.
Divide batter among 12 paper lined muffin cups, filling each to the top (about 1/3 cup in each), then bake in preheated oven 17 - 20 minutes, until toothpick inserted into center comes out clean (or with a few moist crumbs. Tent with foil near end if needed).
Cool in muffin tin several minutes, then transfer to a wire rack to cool completely. Store in an airtight container.
For the gluten-free flour blend: 1 1/2 cups white rice flour* 1/2 cup potato starch 1/4 cup tapioca flour 3/4 tsp xanthan gum*All measurements are to be scooped from package and leveled. Add all ingredients to a mixing bowl and whisk for 30 seconds. Measure what is needed for recipe.Recipe adapted loosely from King Arthur Flour