Preheat your oven to 350°F. Grease or line a standard 12-cup muffin tin and set it aside.
In a large bowl, place the flour, xanthan gum, cornstarch, baking powder, baking soda, salt and sugar, and whisk to combine well.
Create a well in the center of the dry ingredients, and add the butter, eggs, buttermilk, vanilla and mashed bananas, and mix until just combined. The mixture be lumpy because of the bananas, and thick but soft.
Fill each of the wells of the muffin tin, and shake back and forth to evenly distribute the batter in each well.
Place the muffin tin in the center of the preheated oven. Bake until the muffins spring back when pressed gently in the center, 20 to 22 minutes.
They’ll brown nicely around the edges, but not much on top. Remove the muffins from the oven.
Allow them to cool in the tin for 5 minutes before transferring to a wire rack to cool completely. Repeat with the remaining muffin batter.
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Notes
Recipe originally published on the blog in 2016. In 2018, the recipe was scaled up for larger muffins. In 2023, text resources added and some images new.