In the bowl of a stand mixer, use the whisk attachment to beat the room-temperature butter on medium speed for 6 minutes until fluffy and lighter in color.
Slowly pour in one-third of the condensed milk mix until fully incorporated into the butter but not much more.
Continue with another third of condensed milk, allowing it to be fully incorporated before adding the final third.
Add the vanilla and beat until fully mixed in. That’s it. So easy.