To freeze the muffins, wrap them individually in aluminum foil and store in a zip-top bag for up to 3 months.
Preheat oven to 350 degrees. Line a mini muffin pan with paper liners.
In a large bowl, combine banana puree, brown sugar, oil, and egg, beating until smooth. Add flours, baking powder, baking soda, cinnamon and salt and mix well. Add sour cream or yogurt and vanilla; mix to combine.
Fill muffin liners 3/4 full. If you like, place a slice of banana on each muffin. Bake until a toothpick inserted into center comes out clean, about 20 minutes. Transfer to wire rack to cool.