Preheat the oven to 170°C and line two cupcake pans with 24 cupcake liners.
Place the oil, eggs, and sunflower oil in a bowl of an electric mixer fitted with a whisk attachment. Beat at medium-high speed for about 3 minutes until light in color.
Sift together the flour and the salt.
Add the flour mixture to the egg mixture, at once. Beat briefly until just combined.
Add the vanilla to the milk in a jug and slowly pour the milk mixture into the cupcake batter, with the motor of the stand mixer running at medium-low speed.
Once the milk has been added, scrape down the sides of the bowl and mix again briefly. Ensure there are no lumps in the batter.
Fold through the funfetti sprinkles using a rubber spatula.
Pour the cupcake batter into a jug and fill each cupcake paper ¾ of the way full. Bake in a preheated oven for 12 - 15 minutes until a toothpick inserted into the cupcake comes out clean. Allow the cupcakes to cool before decorating.
Marshmallow Frosting
To make the marshmallow frosting, add the sugar and the egg whites to a bowl of a double boiler set over medium heat.
Whisk continuously until the sugar has melted and the mixture is warm to the touch.
Transfer the mixture to a bowl of an electric stand mixer fitted with a whisk attachment. Beat at high speed for about 10 minutes. The frosting is ready when it is white, voluminous, and glossy.
Transfer the meringue frosting to a piping bag fitted with your chosen nozzle and pipe a swirl on each cupcake. Decorate with sprinkles and enjoy!