Preheat oven to 185ºC /365ºF.

Take a big bowl and pour the melted butter in it. You can also use normal butter at room temperature.

Then add sugar and beat it until airy.

Add the eggs to it and beat until fluffy.

Take another bowl and sift all purpose flour into it. Then add baking powder and vanilla sugar to it. Mix well.

Now add this mixture to the beaten egg with few drops of vanilla extract and slowly mix using a spatula so that it does not lose the airiness.

Add orange zest to the mixture.

Mix and pour into cupcake forms equally.

Keep it in the preheated oven for around 15 minutes( time might vary based on the oven type and settings you have).

Once done (check by inserting a tooth pick in the middle of the cupcake and it should come out clean) cool it and serve with some cream cheese topping.