Prepare Your Oven and Tin: First, preheat your oven to 220°C (200°C fan). Line a 12-hole muffin tin with paper cases. The initial high heat is crucial for getting a good rise.

Combine the Dry Ingredients: In a large mixing bowl, whisk together the plain flour, caster sugar, baking powder, bicarbonate of soda, and salt. Whisking helps to aerate the mixture and ensure everything is evenly distributed.

Combine the Wet Ingredients: In a separate medium bowl or large jug, whisk the eggs lightly. Then, add the buttermilk, vegetable oil, and vanilla extract and whisk until everything is just combined.

Mix the Batter: Pour the wet mixture into the bowl of dry ingredients. Using a rubber spatula, fold the ingredients together until they are *just* combined. I find that about 10-12 folds is usually enough. Do not over-mix; the batter should be lumpy and thick.

Add the Blueberries: Gently fold in the flour-coated blueberries until they are just distributed throughout the batter. Be careful not to crush them.

Fill the Muffin Cases: Divide the batter evenly among the 12 prepared paper cases. An ice cream scoop works wonderfully for this, ensuring each case is filled to the top for a generous muffin.

Add the Topping: Sprinkle the top of each muffin generously with demerara sugar. This will create a lovely crunchy crust as they bake.

Bake the Muffins: Place the muffin tin in the preheated oven and bake at 220°C (200°C fan) for 5 minutes. Then, without opening the oven door, reduce the temperature to 180°C (160°C fan) and continue to bake for another 15-20 minutes.

Check for Doneness: The muffins are ready when they are golden brown on top and a wooden skewer or cake tester inserted into the centre comes out clean or with a few moist crumbs attached.

Cool: Let the muffins cool in the tin for 5 minutes before carefully transferring them to a wire rack to cool completely. They are delicious warm, but allowing them to cool helps the texture set properly.