Preheat and Prepare: Preheat your oven to 200°C (180°C fan). Line a 12-hole muffin tin with paper cases.

Combine Dry Ingredients: In a large bowl, whisk together the plain flour, bicarbonate of soda, baking powder, ground cinnamon, and salt. This ensures the leavening agents are evenly distributed.

Prepare Wet Ingredients: In a separate medium bowl, mash the ripe bananas with a fork. I like to leave a few small lumps for texture. Whisk in the melted butter, light brown sugar, egg, vanilla extract, and buttermilk until just combined.

Combine Wet and Dry: Pour the wet banana mixture into the bowl of dry ingredients. Using a spatula, fold the ingredients together until they are just combined. You should still see a few streaks of flour; this is okay. Do not overmix!

Add the Nuts: Gently fold in the chopped walnuts, being careful not to stir the batter too much.

Fill the Muffin Cases: Divide the batter evenly among the 12 muffin cases. They should be about three-quarters full. I find that using an ice cream scoop is the cleanest and most efficient way to do this.

Add the Topping: Sprinkle the demerara sugar evenly over the top of the batter in each muffin case. This will create a lovely, crunchy top.

Bake to Perfection: Bake for 18-22 minutes, or until the muffins are risen, golden brown, and a skewer inserted into the centre of one comes out clean or with a few moist crumbs attached.

Cool Down: Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely. They are delicious warm but will hold together better once cooled.