Preheat oven to 180°C / 350°F. Line or grease a muffin tin.
In a large bowl, mix all dry ingredients: banana peel flour, almond/buckwheat flour, baking soda, baking powder, cinnamon, nutmeg, and salt.
In another bowl, whisk wet ingredients: mashed banana, eggs, syrup, milk, oil, and vanilla.
Combine wet and dry ingredients. Stir until just mixed. Fold in any extras like chocolate chips or nuts.
Spoon into muffin cups about ¾ full.
Bake for 18–22 minutes, or until a toothpick comes out clean.
Cool on a rack, then enjoy warm or store in an airtight container for up to 3 days.