So asks reader Pepper. That’s a good question. I presume what you’re really asking, Pepper, is how a mixture of flour, milk, butter and powdered sugar manages to stand in so well for a standard buttercream. The truth of the matter is that there’s not all that much difference between a heritage “cooked flour” buttercream and a standard buttercream, save for the fact that heritage frosting replaces half the butter — a fat and water emulsion — with a starch “gel”.
Under the hood these two mixtures don’t have a whole lot in common. One is mostly fat with tiny water droplets dispersed throughout. The other is mostly water with a network of string- and branch-like starch molecules tangled up in it. The thing they have in common is that they’re both firm (or relatively so) when they’re chilled or at room temperature, yet they both melt around body temperature. Beat them together with some sugar and you get a stable emulsion which, despite its rather odd composition, feels remarkably silky when you put it in your mouth.
It’s an ingenious concoction. How cooks of yesteryear hit upon it is anyone’s guess. Probably just a lot of trial and error brought on by the necessity of finding a fat substitute when butter was either too rare or too expensive to use.