Preheat the oven to 180c.
Line a 12-hole muffin tin with paper liners and set aside.
In a jug, combine buttermilk, melted butter, vegetable oil, egg, and vanilla.
250 ml buttermilk, 60 g salted butter, 1 egg, 2 teaspoon vanilla, 4 tablespoon vegetable oil
Lightly stir with a fork to combine (it will look curdled, don't worry - that's ok) and set aside (our wet ingredients).
In a large bowl, place self-raising flour and raw caster sugar and whisk to combine (our dry ingredients).
375 g self-raising (self-rising) flour, 220 g raw (golden) caster sugar
Pour the wet ingredients into the bowl with the dry ingredients and then mix to incorporate - it's important not to over-mix the batter.
Divide the mixture evenly amongst the holes of the prepared muffin tin.
Spoon 2 teaspoons of Nutella on top of each muffin, pushing it down slightly into the batter (it doesn't need to be pretty!).
130 g Nutella chocolate hazelnut spread
Take a toothpick or a skewer and swirl the Nutella through the batter a little then bake for 20 - 25 minutes or until a skewer inserted into the middle comes out clean.
Place muffins onto a wire rack to cool.