In a stand mixer with the whisk or paddle attachment, beat the butter on high speed for at least 5 minutes, until the butter has lightened in color and is thoroughly whipped.

Using the tip of a sharp knife, scrape the vanilla seeds into the butter and beat to incorporate.

Add 1 cup of the sugar and begin mixing on low speed to combine, then beat on high speed or about 2 minutes.

Repeat this process 1 cup at a time until all the sugar has been added. Add milk a dash at a time if the mixture becomes too thick or dry. Scrape down the sides as needed and make sure no sugar is visible.

The frosting will last for 1 month in the freezer, 2 weeks in the fridge, and 3 days at room temperature.