Add the room temperature butter to a bowl of a stand mixer or a handheld mixer with the whisk attachment. Mix on a high speed for about 30 minutes until the butter is fluffy and pale in colour. If you live in a hot and humid country, this might be quicker.This should resemble a whipped butter texture and white in colour.
Sift the icing sugar, directly onto the butter. Mix it well for 5 minutes at high speed until it is thick and creamy
Add in the vanilla essence and the milk, colouring if using any and beat it on a medium speed for another 5 minutes.This will ensure you will get a fluffy and creamy buttercream.