I've made it at least 10 times and never had a problem. Whisking the flour into the milk thoroughly before heating will eliminate lumps. I've used both granulated sugar and powdered in this recipe and found that if the air is humid, the granulated will result in a grittier frosting. But the flavor is to die for regardless! The appearance of the milk/flour mixture is a bit off-putting once it's cooled, but once it's mixed with the butter/sugar, it's beautifully smooth and fluffy.
Light, fluffy and delicious frosting. I was a little hesitant after reading some of the reviews but thought I would give it a try. I cooked and whisked the milk/flour mixture until it was a very thick paste. I transferred it to a bowl, covered and refrigerated while I started whipping the butter and sugar. I used Bakers Ultra Fine Granulated sugar which was the perfect choice.
Not too sweet or gritty. After whipping the sugar and butter, I added the milk mixture (which I briskly stirred to remove any new lumps) and allowed it to whip for an additional 7-8 minutes. At the end I added the vanilla, and a pinch of salt to balance. It couldn't be better!