Preheat oven to 180 degrees Celsius (fan-forced) or 355 degrees fahrenheit.
Line a 12-hole muffin tin with paper cases and set aside until needed.
Sift the self-raising flour into a large bowl.If using a Thermomix: Place the self-raising flour into the Thermomix bowl and sift 5 seconds, Speed 8.
Add the caster sugar and stir together.If using a Thermomix: Add the caster sugar, egg, vegetable oil and milk and mix for 5 seconds, Speed 5. Scrape down the sides of the bowl and repeat for a further 5 seconds, Speed 5. The batter should be slightly lumpy.
Create a well in the centre of the dry mixture.
In a separate bowl, lightly beat the egg before adding the vegetable oil and milk and whisking together until well combined.
Pour the liquid ingredients into the well in the dry ingredients, and very gently fold the mixture together. The batter should be slightly lumpy; don't over-mix.
Very gently fold through the white chocolate chips.If using a Thermomix: Use the spatula to gently fold the white chocolate chips through the muffin batter.
Spoon the mixture into the paper cases, filling halfway to the top.Use a teaspoon to make an indent in the centre of the mixture and add a heaped teaspoon of Nutella (reserve ⅓ cup of the Nutella for swirling over the top). Add the remaining muffin batter to the top of the muffins.
Heat the remaining ⅓ cup of Nutella in the microwave for 30 seconds or until softened. Divide the Nutella to the top of the muffins and use a skewer or butter knife to gently swirl it around.
Sprinkle the top of the muffins with caster sugar or raw sugar (optional).
Bake for 20-25 minutes or until lightly golden.
Allow to cool in the baking tray for 5 minutes before transferring to a wire rack to cool completely.
Notes
RECIPE NOTES & TIPS:
It's important to not over-mix the muffin batter as it will make your muffins tough... we want them nice and light! Gently fold the ingredients together - a few small lumps are fine.