Step 1

Beat the butter until smooth and fluffy.  Be sure to scrape the sides of the bowl and the beaters a couple of times to ensure there are no lumps left in the butter.

Step 2

Add a couple of Tablespoons of cold sweetened condensed milk and the vanilla. Beat until it is well incorporated.

Step 3

Add the remaining sweetened condensed milk, a little at a time and beat for at least two minutes.

Step 4

Spread or pipe on cake or cupcakes. If desired, chill to set.