Preheat the Oven: Set the temperature to 375°F (190°C).
Whisk dry ingredients: Add all of the dry ingredients, such as cake flour mix, all-purpose flour, baking powder, baking soda, salt, and brown sugar, to a large bowl.
Combine wet ingredients: In a separate bowl, add the Mashed banana, buttermilk, oil, whisked egg, and vanilla essence.
Mix ingredients: Mix the wet into dry ingredients. When it comes to muffin mix, it is okay to have a few lumps here and there. Overmixing will result in a dense muffin. Use an ice cream scoop or spoon to divide the batter into muffin cups. Fill them until they reach 3/4 full. If you want a large bakery-like muffin, fill the cupcake liner to the top and skip one every other muffin.
Bake: Bake for 30 minutes or until a toothpick inserted into the center comes clean. Cool for 5 minutes in the pan, then transfer to a wire rack to cool completely.