ASB Basics: Swiss Meringue Buttercream (Intermediate)
2 Cups, 4 regular sticks (452g) good quality unsalted butter at room temperature, cut in cubes. (I cut my butter when it is cold, then leave it out on the counter, covered, for several hours.)
1 cup + 2 tbsp (230g) granulated sugar
5 egg whites at room temperature (I find them easier to separate when they're cold and let them come to room temperature in the mixing bowl. Separate the eggs in different bowls to ensure no yolk gets in your whites before transferring the mixing bowl. Save your yolks to make ice cream, custard, or lemon curd.)
Small pinch of salt
Bring a small pot with about 1 inch of water to a boil, then reduce to a simmer.
Place the metal bowl of a stand mixer containing the sugar, egg whites, and salt over the pot (make sure the bowl does not actually touch the water below)
Whisk constantly for 2-3 minutes until the sugar is completely dissolved into the egg whites. To test, dip clean fingers in the mixture and rub them together. If you can feel little sugar granules, you need to keep going. By the time it is ready, your egg white mixture will be foamy.
Remove the bowl from heat, and place it on your stand mixer fitted with the whisk attachment.
Starting briefly on low, moving gradually to medium-high speed, beat for 10 entire minutes. You'll notice by the time the 10 minutes are up, your warm bowl will be at room temperature.
Reduce the speed to medium-low, and add in the butter with the mixer running about 1 tbsp at a time. After each 1 tbsp addition, let the butter incorporate mostly (about 15 seconds) before adding more. If your buttercream looks broken, don't worry--keep going, it should eventually come together. However, if all your ingredients start at room temperature, you should not encounter this problem.
Once all the butter is added, scrape down the bottom and sides of the bowl and mix on low for a minute or two until everything is evenly combined. This also the point at which you can add your favorite flavorings like vanilla extract, melted and cooled chocolate, or salted caramel.
If you plan on using your buttercream the same day, no need to refrigerate. Otherwise you can refrigerate for a few days or freeze for a few weeks. To thaw, remove from refrigerator and let come to room temperature. Beat for a few minutes until it returns to the normal texture. To thaw from frozen, switch to the refrigerator overnight, then do the same.