1. Using a hand mixer/electric mixer/whisk, beat the butter for about 5-7 minutes till smooth and pale.
2. Add vanilla essence and mix well.
3. Sift the icing sugar and cocoa powder together. Now gradually add the icing sugar-cocoa mixture to butter while beating it. Ensure all sugar and butter is mixed well.
4. Add milk and beat the mixture until light and fluffy. You can add more milk or icing sugar depending on the consistency of the frosting.
5. Transfer the icing to a piping bag with a nozzle of your choice for frosting cakes or cupcakes. Ensure your cakes/cupcakes are cool before you start piping.

Notes – 

1. The consistency of the frosting might differ depending on the kitchen temperature and quality of ingredients. Hence, the icing sugar and milk should be adjusted depending on the final texture – if it’s too dry add a teaspoon of milk, if it’s wet, add a tbsp of icing sugar and go from there.