Swiss Meringue Buttercream

Be prepared to have leftover egg yolks.  Fortunately, I was going to make some lemon curd anyway.  If I make this again, there will be a new ice cream flavor.

This is that frosting that feels like it's made with whipped cream.  Soft and silky, ridiculously pipeable, and not quite as sweet as a regular buttercream.

Older cookbooks and your grandma's recipe box call this seven-minute frosting, because it takes about seven minutes of whipping the meringue for it to cool to room temperature.  You start by heating the egg whites and sugar to about 160º over a double boiler.  This melts the sugar and semi-pasteurizes the egg whites.  If they were completely pasteurized, they wouldn't whip.  Then you let them cool down as they're being whipped into meringue (over a bowl of ice water if it's a very hot day) before beating in the butter and extract.

And that's it.  Not as temperamental as an Italian buttercream (boiled frosting), you just have to keep stirring over the water bath so you don't make an egg white omelet in step 1.  Any lumpy breakage after the butter is incorporated can be fixed by continued whipping.  And whipping, and beating, and more beating.  Seven minutes, my butt.

This version is from The Pioneer Woman because it was the smallest yield I could find and I only made a 2-layer, 6" cake, plus this wasn't the filling.  There are larger recipes out there, including the 7 egg-white recipe that I nixed because it used a prime number of eggs.  This one has round numbers that can be doubled or halved with minimal baking math.  The yield was enough for a crumb coat and a really thick layer of decorating.  And I probably had enough scrapings left that I could have filled the cake with it after all.  If you're making a less ornamental cake, it will likely do an 8", 2-layer.

You may notice the Passover label on this recipe.  Unlike other frostings I've used, this one does not rely on powdered sugar.  You do need to check the vanilla extract for a KLP designation, or make vanilla sugar ahead of time with a whole vanilla bean.  Next up, finding a Passover cake recipe that doesn't suck.  My birthday falls during the holiday about a quarter of the time, so this is a lifelong struggle for me.

4 egg whites
1-1/2 C granulated sugar
1-1/2 C (3 sticks) unsalted butter
1 tsp vanilla extract, or more to taste
pinch of kosher salt

1.  Set up a saucepan with 2" of water in it over medium-low heat to a light simmer.  NOT a full boil. Over it, set the bowl of the stand mixer and make sure the water does not touch the bottom of the bowl.

2.  Whisk together the egg whites and sugar to combine.  They're going to be very thick and grainy.  Whisk the mixture lightly but constantly as it heats to 160º.  Scrape the sides of the bowl often.  This is going to take a minimum of 15 minutes.  When ready, you won't be able to feel any sugar grains when you rub some between your fingers.

3.  Attach the bowl to the mixer and whip with the whisk on medium-high until room temperature.  It was a warm day, so this took more like 20 minutes and was aided by a bowl of ice water under the mixer.  In the winter, you can do it in seven.  While that's going, start softening the butter to room temperature as well.  Do some dishes, stretch out the shoulder you got sore by all that whisking, etc.

4.  When meringue is ready, switch to the paddle and start dropping in the butter one tablespoon at a time.  If the butter and meringue are the same temperature, it will mix in fairly quickly.  When one is warmer than the other, it may get clumpy.  Just keep beating it if that happens, and it will eventually mix in properly.  Beat in vanilla and salt to finish.  If it gets soupy, put it in the fridge for two minutes to firm up the butter, then paddle it again.

5.  The finished frosting can be used immediately, or refrigerated for later.  If refrigerated, it should be left at room temperature for an hour and then beaten back into softness.  Once on a refrigerated cake, let it come back up to room temperature for a minimum of an hour before serving.

Makes enough to frost and fill one 8" layer cake

Difficulty rating  :)