Start by whipping the softened unsalted butter at high speed using a stand mixer or handheld mixer for approximately 10 minutes, until it becomes very light and fluffy, and has nearly tripled in volume. Be sure to scrape down the sides of the bowl with a spatula as necessary.

Once the butter achieves a fluffy consistency, gradually add the sweetened condensed milk in 3 or 4 increments, mixing thoroughly after each addition and scraping the bowl as you go. You can adjust the amount based on your desired flavor and thickness, so it’s not necessary to use the entire can.

If the frosting seems to have separated or curdled, place it in the refrigerator for 15-20 minutes, then re-whip it until the texture becomes smooth again.

Finally, incorporate the optional vanilla extract and salt if desired, and your frosting is ready to be spread on cakes and cupcakes. Enjoy!