Preheat the oven to 350ºF and line a muffin tin with 12 muffin cups.
In a large bowl, combine the mashed banana, sugar, almond butter, flour, baking powder, vanilla, and salt and stir well until the batter is relatively smooth. (You can do this in a food processor, if you want an ultra-smooth batter with no chunks of banana, but I usually just stir it together by hand.)
Divide the batter among the 12 muffin cups, using roughly a scant 1/4 cup measure. The cups should be only 1/2-3/4 of the way full. Bake at 350ºF until the muffins rise and feel firm to a light touch in the center, about 25 to 30 minutes.
Let the muffins cool completely, then enjoy. You can store these muffins at room temperature for up to 2 days, but they will dry out over time, so I recommend keeping them in an airtight container in the fridge for up to a week, instead. They also freeze well if you want to make extra!
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Notes
This recipe works best with a gluten-free flour blend, not a single gluten-free flour, like oat flour or almond flour. If you need a nut-free recipe, try using sunflower butter or tahini in place of the almond butter.