Add the sugar and eggs to a bowl and use a hand mixer to beat them well until you have a pale yellow colour and they triple their volume.
In a pan set over a low to medium heat, add the milk and butter cut into cubes, and heat them up until the butter is melted.
Pour the milk mixture over the egg mixture whisking really well.
Sift in the flour and baking powder, and the vanilla extract, and mix well to get a runny batter.
Line 12-hole muffin tray with non-stick muffin cases, and divide the batter evenly.
Bake in the preheated oven at 180 degrees Celsius (350 Fahrenheit) for 20 minutes or until golden and a skewer inserted in the middle comes out clean.
Remove the cupcakes from the oven and set them side to cool down completely.
To make the buttercream, add all the ingredients to a food processor, and blitz to get a smooth and silky buttercream.
Use a piping bag fitted with a start nozzle (or any other nozzle of your choice) to decorate each cupcake.
You can also use some sprinkles if you wish.