While it may sit on a relatively obscure branch of the buttercream family tree, flour frosting is among the easiest to prepare—no eggs or meringue, candy thermometers, or powdered sugar in sight.
Flour frosting is a starch-thickened, milk-based frosting made with granulated sugar, giving it some broad similarities to German buttercream in terms of both flavor and technique. But flour frosting is eggless, so there's no custardy flavor or yolk-y color—only the clean taste of fresh milk and butterfat (a combination that, unsurprisingly, tastes much like whipped cream).
Flour frosting feels as soft, fluffy, and luxurious as a billowing fur coat, which is perhaps how it came to be called "ermine frosting" in some parts of the country, where it's the traditional finish for a red velvet cake.
Personally, I'm fond of letting its simplicity provide an element of contrast with boldly flavored cakes, like chocolate and strawberry, but its creamy richness can just as easily highlight the primary flavors of a classic vanilla cake.
Virtually all recipes approach flour frosting in one of two ways. Some will have you cook the flour and milk together until thick, then whip the cooled paste with granulated sugar and butter. Others call for cooking the flour and milk together with the sugar, then whipping the cooled paste with butter.
The former yields the best flavor and body, but frosting made this way often contains a trace of grit from undissolved sugar crystals. The latter results in the silkiest texture, but because sugar alters the boiling point of milk, the flour isn't as thoroughly cooked, giving the frosting a starchy aftertaste and comparatively loose body.
Happily, I've found that it's easy enough to split the difference in technique, for a flavorful, full-bodied frosting free of any grit or starchiness. It starts with all the same ingredients: flour, sugar, and milk, plus a little salt.
I start by whisking the flour and milk until smooth, then boiling them together. This ensures the flour is fully cooked, eliminating its starchy flavor and forming a thick, roux-like paste.
When the flour-milk paste is fully cooked, I shut off the heat and add the sugar so it can dissolve into the warm mixture. Because this step liquefies the sugar, the mixture will seem runny and thin, but rest assured that the flour's thickening power has not been compromised.
I set the mixture aside and allow it to cool to about 70°F (21°C). Meanwhile, I warm the butter until it's pliable and soft, but still cool to the touch, about 65°F (18°C). This can be done passively over time on the counter, or with a few controlled bursts in a microwave.
Either way, it's less about achieving some laser-precise temperature than it is about quantifying a more useful ballpark figure than "room temperature." The idea is to have butter that is neither rock-hard from the fridge nor squishy from sitting out all day.
Using a stand mixer fitted with a paddle attachment, beat the butter until it's creamy, light, and soft, but not loose. In my kitchen, this takes about five minutes.
As with any recipe, the listed time is an approximation, not a goal. Times are meant to contextualize, not constrain, a physical process. The only goal is to achieve the visual and textural cues described.
Once the butter is soft and light, begin adding the cooled milk paste, a little at a time.
Continue beating the frosting until it's homogeneous, pausing to scrape the bowl and beater as needed.
When the frosting looks perfectly smooth, switch to a whisk attachment, and whip until it's airy and light.
As with any buttercream, the final stage of whipping will likely require some adjustment to reach the appropriate temperature. A soft, loose buttercream will need to be chilled, while a dense, heavy, greasy, or curdled buttercream will need to be warmed.
This is normal! However precise a recipe may be in terms of target temperatures (for both the ingredients and the finished product), the ideal working temperature of a buttercream can vary from batch to batch, depending on environmental conditions and the time of year, as well as variations in equipment and ingredients.
So, rather than rely on a thermometer alone, evaluate the texture and consistency of the frosting. If it's heavy and dense, if it has a greasy texture, or if it seems curdled, it will need to be warmed and re-whipped. If it seems too soft or loose to hang from a spoon without dropping, it will need to be cooled and re-whipped. These are routine adjustments, not a sign of failure. (For more specifics, check out my buttercream troubleshooting guide—though it was originally designed with Swiss buttercream in mind, these methods will work for any buttercream.)
When the temperature and texture of the frosting have been properly adjusted, it can be seasoned to taste with additional salt, as well as vanilla extract (or whatever other extract you prefer).
Flour frosting may not be as sturdy as a German buttercream or as airy as a Swiss one, but it's a wonderful alternative when circumstances, or dietary considerations, rule out the use of eggs.
Likewise, ermine may not be as quick and easy as a traditional American buttercream, but it avoids the use of powdered sugar. What's more, flour frosting contains less sugar than any other buttercream style, so it can bring balance to sweeter cakes or those meant to be served à la mode.
Thanks to these attributes, along with its uniquely cream-like flavor, flour frosting has more than earned its place in my recipe repertoire, and I hope you'll find it just as useful.