4tablespoonsunsalted butter, cut into about 8 to 10 chunks, cool room temp.(56 grams)
⅛ teaspoonsalt
½teaspoonvanilla extract
Instructions
In a small nonstick saucepan, mix together the sugar and cornstarch. Add the cold milk and whisk mixture to dissolve the cornstarch. Set over medium heat and cook, stirring constantly with a heat-proof rubber scraper, until the mixture begins to form big bubbles and thickens. It will stick to the side of the saucepan.
Without scraping the film from the side of the saucepan, scrape the mixture into a shallow bowl. Press a piece of greased plastic wrap directly against the surface, and let cool for about 1 hour.
Note: This is a good time to take the butter out of the refrigerator, cut it into chunks and let it sit for an hour.
Remove plastic wrap and scrape the mixture into the bowl of a stand mixer with the whisk attached. Begin beating on medium speed. With the mixer going, add butter 1 or 2 chunks at a time letting it dissolve into the mixture. When all the butter is incorporated, add the salt and vanilla and beat on medium high until mixture is pale and creamy.
At this point the mixture might look a little soft and shiny. Remove the bowl from the stand, scrape any icing that is sticking to the whisk attachment into the bowl, then put the whole bowl in the freezer for 10 minutes.