This whipped icing is the one my grandmother always used for her richest, most decadent cakes because it's light, creamy and not overly sweet. Ermine frosting is easily spreadable and tastes like the best whipped cream frosting you've ever had (but there's no cream in it).
Add the milk and flour to a small saucepan and whisk to combine. Heat over medium to medium high heat, whisking constantly until the mixture gets very thick with an almost gluey texture. Remove from heat and cool to room temperature. As the flour and milk mixture cools is will become pudgy and very thick to the point that it's almost difficult to stir.
In a large bowl, combine the butter, sugar, vanilla and salt. Beat with an electric mixer until very light and fluffy, about 2-3 minutes. Add the cooled milk mixture to the butter and beat on high speed for 5 minutes, scraping down the sides of the bowl occasionally.
Transfer the icing to the refrigerator for 5 minutes.
Remove the icing from the refrigerator and beat again until thick and creamy, about 1-2 more minutes.
Before frosting cakes or cupcakes, ensure that they have cooled to room temperature.
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Notes
This recipe will frost a standard size 9" layer cake, 9x13 sheet pan or 24 cupcakes.