I finally got my cooked custard frosting right, but instead of turning off the mixer and acknowledging my success, I continued to beat the icing, which in turn caused the butterfat to separate slightly from the rest of the icing (resulting in a not totally smooth icing with pockets of melted butter). Does anyone have any suggestions for whether I could add an ingredient or do something to make this frosting come back together and not appear greasy? It's not so bad that I couldn't use it as is, but it also isn't perfect. Thanks!
p.s. For anyone who isn't clear, this is the icing that involves heating milk and flour, allowing that mixture to cool, and then adding it to a beaten butter/sugar combination.