Preheat and Prep: Preheat your oven to 220°C (200°C fan). Line a 12-hole muffin tin with paper liners and set it aside.

Combine Dry Ingredients: In a large mixing bowl, whisk together the plain flour, cornflour, baking powder, bicarbonate of soda, salt, and caster sugar. Breaking up any lumps now ensures a smoother batter later.

Combine Wet Ingredients: In a separate medium bowl or a large jug, whisk the melted butter, vegetable oil, eggs, and vanilla extract until well combined. Then, stir in the buttermilk.

Gently Mix Batter: Pour the wet ingredients into the bowl of dry ingredients. Using a spatula, fold everything together until it is just combined. The batter will be thick and lumpy – this is what you want! Do not be tempted to overmix.

Add the Blueberries: Gently fold in the blueberries, being careful not to crush them. If using frozen, add them directly from the freezer without thawing.

Rest the Batter (Optional but Recommended): Let the batter rest at room temperature for 15 minutes. This allows the flour to hydrate and, in my experience, contributes to a better rise and a more tender muffin.

Fill the Muffin Cases: Divide the batter evenly between the 12 muffin liners. They will be quite full, which is key to achieving those high domes. Sprinkle the tops generously with demerara sugar for a lovely crunch.

Bake: 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 190°C (170°C fan) and continue to bake for another 15-17 minutes, or until the tops are golden brown and a skewer inserted into the centre of a muffin comes out clean.

Cool: 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.