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If Swiss buttercream is a rockstar in the realm of frosting, then German buttercream is an indie powerhouse—well loved by its dedicated fans, but relatively unknown to the wider world. For the uninitiated, it's a style that combines thick vanilla pudding with whipped butter for a frosting with loads of structure and stability, plus a milky flavor reminiscent of vanilla soft serve.
That profile makes it my go-to format for any dairy-centric project, whether for cream cheese buttercream or cannoli filling, where the custard's inherent thickness can offset high-moisture ingredients like cream cheese and ricotta. But German buttercream is a wonder all on its own, and deserves a place in any baker's repertoire—particularly those with a soft spot for ultra fluffy frostings.
Because German buttercream incorporates a significant amount of milk into the underlying custard, it's the perfect technique for creating flavorful infusions with vanilla beans, cinnamon sticks, sliced bananas, fresh herbs, or whatever ingredients you'd normally reach for when flavoring ice cream at home (just avoid acidic ingredients that can curdle the milk). The trick is to steep the milk long enough to extract a super-potent flavor that can stand up to the addition of butter down the road, so don't rush the process.
I like to warm the milk with a vanilla bean (or other flavoring agent), then cover and steep at least an hour. But for maximum effect, you should steep it even longer by tossing it in the fridge overnight (or up to 24 hours) to extract a deeper flavor. Sure, it's not the fastest option, but if you're in a hurry that's what Swiss buttercream is for. Whatever the timeline, rewarm the milk at the end of the steeping process and scrape out the vanilla bean (or whatever) to make sure all the flavorful bits make it into the frosting.
If steeping the milk with absorbent ingredients like toasted nuts, or those with lots of nooks and crannies, such as fresh herbs or coffee beans, re-measure the milk and top-it off as needed to account for any loss. Or skip the steeping phase altogether and just use your favorite extract in the finished buttercream, adding it in small increments until you get just the taste you want.
Before getting started on the thick custard base, it helps to have a simple balloon whisk and 3-quart stainless steel saucier (its easy-to-scrape rounded corners make it a favorite in the pastry kitchen). With straight-sided pots, the custard may curdle or scorch in the corners of the pan; normally, that's a great excuse to put a ball-whisk to work, but the thickness of this custard will collapse its tines, making it difficult to emulsify. With the right equipment for the job, the recipe isn't any fuss, but extra vigilance will be in order when adapting it to less-than-optimal gear.
Start by whisking the sugar and cornstarch together in a medium bowl, then add the eggs, followed by the milk (flavored or plain). Pour the mixture into the saucier and cook over medium heat, whisking constantly until thick and steaming hot. It may look a little lumpy and weird early on, but keep whisking until it's silky smooth and bubbling hot.
Once you spot the first bubble, set a timer and keep at it for exactly two minutes; this isn't about reaching a specific temperature (the boiling custard will be, you guessed it, 212°F the whole time) but rather maintaining that heat long enough to help denature a starch-dissolving enzyme found in egg yolks, one that can turn the custard soft and soupy over time.
When the time's up, scrape the finished custard into a baking dish or pie plate and spread into a thin layer to speed the cooling process. Cover the pudding and refrigerate it until thick and cool but not cold, somewhere between 68 and 70°F. Alternatively, it can be refrigerated up to a week in advance then left at room temperature until it warms up to a similar range.
When you're ready to assemble the buttercream, use a sturdy spatula to "knead" the thick pudding until creamy and smooth. That may sound like a weird way to describe the process, but unlike the sort of gooey-soft custard you'd find in a cream puff, the custard base of a German buttercream is meant to provide body and structure to the frosting, so it's nearly as thick as a cookie dough. With a little elbow grease, it'll soften into a creamy paste.
I used to recommend beating the custard in a stand mixer until smooth, but over-mixing at that stage can damage the custard's thickening power, so the safest option is to mix it by hand and beat the butter instead. Start by softening the butter to a similar temperature range, no colder than 68°F but no warmer than 72°F; I do this with a few cautious zaps in the microwave, but it can be done passively at room temperature as well (or, god forbid, sous vide; there, I said it).
Beat the soft butter with the paddle attachment of a stand mixer until creamy and smooth, then start chucking in the custard a few tablespoons at a time (no need to measure), one addition right after the other, and continue beating until no lumps remain. Scrape the bowl and beater with a flexible spatula, then continue beating about 30 seconds more, or until perfectly silken. Thanks to all that friction, beating will warm the cool frosting a few degrees, the ideal set up for phase two—aeration.
Switch to the whisk attachment for this stage, and whip the buttercream until it's fluffy and light.
That phrase may seem a little abstract, but in this case it can be quantified to a certain extent, as a buttercream made with the proper technique should weigh about 6 ounces per cup (this is true of almost any "fancy" buttercream, whether French, Swiss, German, or even the marshmallow-style frosting from my cookbook).
A heavier weight per cup is a surefire indication of a chilly frosting, one stiffened by cold butter unable to stretch and expand with aeration. A few degrees or ounces here or there may sound like a compulsive detail only trained pastry chefs could appreciate, but not so! The differences are night and day.
The two frostings above came from the exact same batch of German buttercream. The only difference? Temperature, and therefore density. On the left, a spoonful of frosting with a final temperature of 65°F and a weight of 8 ounces per cup; on the right, a spoonful of frosting with a final temperature of 72°F and a weight of just 6 ounces per cup.
These differences in temperature and volume affect everything about the buttercream, from sweetness to yield. When cool temperatures prevent proper aeration, the amount of sugar and fat in the recipe will be concentrated into a smaller, denser yield. This cold, dense buttercream will therefore taste sweeter and have a greasy mouthfeel, like a lump of cold butter on your tongue. Not only that, but its density and firmness make it a nightmare to spread over soft cake. Ever scraped cold butter over toast? Not fun.
When the butter is at the correct temperature it will allow the frosting to be properly aerated, and the amount of sugar and fat in the recipe will be stretched across a higher, lighter yield. This makes the buttercream seem less sweet, with a billowy consistency and pleasant richness that melts quickly and cleanly on the tongue. Because it's so soft and light, it's easy to spread over a cake in puffy swoops and swirls.
As drastic as these differences can be, temperature-related problems can always be fixed, and that fix is always easy. If it's too cold and dense, place the buttercream over a warm water bath until the sides of the bowl start to get slick with melted buttercream, then re-whip. If it gets too warm and the buttercream becomes soupy and soft, refrigerate for 15 minutes or so then re-whip. It can be a bit of a balancing act for beginners to find the ideal temperature, but the risk of failure is nil. And once you've done it the right way, it gets easier every time.
For more information, check out our buttercream troubleshooting guide. Though written on the subject of Swiss buttercream, all the same rules apply to German buttercream as well, so there's no reason to ever settle for a buttercream that's heavy and dense.
Because temperature-related problems are so easy to solve, German buttercream can be made in advance and frozen for several months, then thawed in a microwave and re-whipped on demand. With a little attention to detail, it'll turn out soft, creamy, and perfectly fluffy every time, with a mellow sweetness and milky vanilla flavor. Like its French and Swiss counterparts, German buttercream is sturdy enough to support even the most towering layer cake, but its pudding base gives German buttercream a down-home flavor and lightness suitable for even a simple Texas sheet cake as well.