Meringues can be a real pain. But if you get them right, there's nothing better.
What is Swiss meringue buttercream anyway? It is the best of the buttercreams and I'll tell you why. French buttercream (whole eggs + egg yolks + cooked sugar syrup + butter) is awesome but super rich and the least stable of the bunch. Italian buttercream (egg whites + cooked sugar syrup + butter) is lighter and the most stable; it will stand up to heat the longest. So again, why use the Swiss style? Well, it's also very stable and is SMOOTH AS SILK. It's great for filling and finishing wedding cakes and is just delightful. It is more susceptible to warmer temperatures than its Italian counterpart, but my version holds up pretty well (I live in Florida. I know things about heat and humidity). Another reason SMBC (swiss meringue buttercream) is a winner, is that it's a bit easier to handle than Italian buttercream (pouring hot sugar syrup into whirling egg whites is not for the faint of heart, but it's also not impossible.). For a lovely little primer on types of buttercreams, read this Craftsy article.
I've adjusted how I make it over the years. I used to use this recipe by Martha Stewart but I found it wasn't quite stiff enough for my swampy Floridian environs. Also, this recipe is written "by volume" and I'm more of a "by weight" gal, myself.
I'm also stickler for temperatures. When people suggest checking something by feel, I get it--touch is an important sense to develop in the kitchen, but I need a temperature (at least a close one) to associate it with. Benchmarks are everything. So, some say the sugar syrup for SMBC is ready when it feels like a hot bath (on a personal note, I'm not really a bath person, so this was not super helpful). Martha says cook it until it's warm and the sugar has completely dissolved. BUT WHAT TEMPERATURE IS THAT?
Traditionally this number clocks in around 160-ish degrees Fahrenheit. But, it is our friends at Serious Eats (actually its Stella Parks of BraveTart fame) who gave me a good tip: cook the sugar and egg whites to 175 degrees F.
Excellent! Not only does this mean that the egg white sugar syrup is fully cooked, it means it's a little bit stronger and stiffer. It means the syrup has some chutzpah.
A good recipe is all about ratios. How many egg whites, to sugar, to butter are you using? Every version varies a little bit, and here is mine. I find this works quite nicely and it's as easy as 1, 2, 3. Here's my recipe for "1, 2, 3 Swiss Meringue Buttercream":
1) Egg whites. 200 grams. This is roughly 6 or 7 large egg whites.
2) Sugar. 400 grams. Notice how it is double the amount of egg whites.
3) Butter. 600 grams. It's like a pound and half-ish. Notice how this is triple the amount of egg whites.
4) 1/4 teaspoon of fine sea salt
The beauty of this is that you can always make this buttercream by simply making your egg whites the base of your ratio, 1, and multiplying that number by 2 to get your sugar and 3 to get your butter. So for instance, let's say you have 100 grams of egg whites, that means you need 200 grams of sugar and 300 grams of butter.
NOTE: Before you get started here, make sure that your whisk and the bowl are extremely clean. Any dirt or fat residue left behind will guarantee your meringue never comes to fruition.
1) Combine the egg whites and sugar in the bowl of stand mixer and set if over a double boiler. Cook, stirring occasionally to 175 degrees F.
2) Place the bowl into the stand mixer and whisk, on super duper high, until that meringue is stiff, glossy and the bowl is cool. Pro tip: Make sure the bowl is cool otherwise your butter is going to melt and you'll just have Swiss meringue soup instead. And then you'll be sad.
3) Once the bowl is cool, your meringue (which you can use for any old meringue need at this point btw) is light as a feather and stiff as a board, go ahead and start throwing in small chunks of room temperature butter on low speed. If you're frosting is still a bit warm and therefore a little loosey-goosey, apply a couple of ice packs to the outside of the bowl with the mixer on medium-low. It should set up properly quite quickly.
And then BOOM.
Swiss. Meringue. Buttercream.
And that's it. That's everything.
Almost. If you're a little intimidated by weighing ingredients, don't be. Get yourself a kitchen scale and save yourself from inaccurate ratios. Here's a great option that, I have in my own kitchen, that's available on Amazon: