Preheat the oven to 350°/180°C or 160°C fan oven, and line a muffin pan with muffin liners. Set aside.
Combine dry ingredients in a bowl (flour, baking powder, baking soda, cinnamon, salt) and set aside.
In a large bowl, whisk together the sugar, egg, mashed banana, melted butter, vanilla.
Add the dry ingredients to the wet ingredients, and stir just until mixed.
Using a large cookie scoop, divide the batter between 12 muffin liners.
Bake for 25-30 minutes or until a toothpick comes out clean from the center of a muffin.
Cool on a cooling rack, serve at room temperature.
Avoid Overmixing: Overmixed muffin batter will create tough muffins that don’t rise in the oven. Stop mixing as soon as the dry ingredients are mixed in.
Be Sure Your Bananas Are Ready: Don’t try to bake with bananas that aren’t ripe enough. Your bananas should look like the ones in my photo above, yellow with a good amount of brown spots on them.
Add Some Fun: You can add chocolate chips, oats, nuts, or dried fruit to the batter to make these muffins extra special. I suggest adding no more than ½ cup of any add-ins. If you are adding oats, add a splash of milk as well to keep the batter and the muffins moist.
Fill Muffin Cups Only Halfway: If the muffin cups are too full, the batter will rise up and overflow in the oven. Use a cookie scoop or a small measuring cup to get evenly filled muffin cups.
Freezing: Simply wrap each muffin in plastic wrap, then place them all in a plastic freezer bag. Eat them within two months for best results.