• Preheat: Preheat the oven to 400°F (200°C), or 180°C convection. Line a 12-cup muffin pan with liners.
• Flour mixture: In a bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon and sugar.
• Banana mixture: In a separate large bowl, mash the banana until mostly smooth. Add the eggs, oil, buttermilk and vanilla and whisk until combined.
• Combine: Add the flour mixture to the banana mixture. Fold gently just until combined. The batter should be thick and fall from the spatula in a thick ribbon.
• Fill: Divide the batter evenly between the 12 liners, filling them almost to the top.
• Sugar Topping: Sprinkle each muffin with a little granulated sugar.
• Bake: Bake for 5 minutes at 400°F (200°C), or 180°C convection.

  Without opening the oven, reduce the temperature to 375°F (190°C), or 170°C convection, and continue baking for another 12–15 minutes, or until well risen and a skewer inserted into the center comes out clean.
• Cool: When the muffins come out of the oven, leave them in the pan for 5 minutes, then transfer them to a wire rack.

Storage

• Keep completely cooled muffins in an airtight container at room temperature for up to 2 days, or refrigerate for up to 5 days.

  Freeze in an airtight container or freezer bag for up to 3 months. Thaw at room temperature for 1–2 hours or overnight in the fridge.