Weigh the required amount of butter, cube it down and allow it to soften.
Once softened in a mixing bowl beat the butter until it is pale yellow or almost white in colour. This would take around 13-15 mins using a hand held mixer and about 8 to 10 mins in a stand mixer. Do remember to stop and scrape the bowl every now and then.
When you observe the evident colour change in the butter, start adding condensed milk a little at a time and beat well before each addition.
Finally, add vanilla essence and mix well. Condensed Milk Buttercream is now ready to be piped.