The decorator's buttercream
Swiss buttercream is my favorite kind for decorating large celebration cakes. Its light texture and delectable flavor, combined with its stability make it a dream for cake decorators and diners alike.
Getting set up
Begin by filling a pot halfway with water. Make sure you use a pot that is large enough to set the stand mixer's bowl over to use as a double boiler. Bring water to a boil. While you're waiting, weigh the egg whites in the mixer bowl until you have the proper quantity. Add cream of tartar and salt, and whisk by hand until the whites are frothy.
Add the sugar
Continue whisking the egg whites and begin slowly adding the sugar as you go.
Whisk, whisk, whisk
Once all the sugar is added, continue whisking. The mixture should get light and the bubbles dense.
Protect your hands
Wrap a towel around the handle of the mixer bowl so your hands don't get burned.
Whisk over the water
Once the water is simmering, place the mixer bowl over the top so it rests on the edges without touching the bottom of the pot. Whisk the mixture vigorously to create the most volume possible. Don't stop mixing or the mixture will overcook in spots.
Continue vigorously whisking the mixture in the bowl over the boiling water. Check the temperature as you go. You'll want to bring it up to 140 degrees, which will make the eggs safe for consumption. If you go any higher, you will overcook the mixture, which will begin to look chunky and dull. If this happens, you will need to start over.
At 140 degrees Fahrenheit
The mixture will look shiny and wet, with dense bubbles. It will still be runny.
Attach the mixer bowl to the mixer
Use protective towels or gloves to handle the mixer bowl, which will be very hot to the touch.
Using the stand mixer fitted with the whisk attachment, whisk the mixture on high until the bowl feels cool to the touch and the meringue holds firm, shiny peaks—this will take 7 to 10 minutes.
Prepare the butter
As the meringue whips and cools, cut the butter into 1 inch pieces. The butter should be cool but pliable.
Add the butter
Once the meringue has cooled (this is important, if it's too warm, the butter will melt), begin adding the butter a little bit at a time. Allow the butter to fully incorporate between additions.
Scrape down the sides
While mixing, stop periodically to scrape down the sides for even mixing.
As you add the butter and whisk, don't be alarmed if the mixture suddenly becomes soupy. Once all the butter has been added, turn the mixer speed up to high and continue to whisk.
The mixture comes together
After whisking on high, the mixture will firm up to the proper consistency. It should look slightly shiny and stand up on its own.
Once the buttercream has achieved proper consistency, lower the mixer speed and add flavored extract or the seeds scraped from the inside of a vanilla bean and whisk until the flavor is completely incorporated.
Add color, if desired
Once the flavoring is completely mixed in, add color gel, if desired. For coloring, gel is preferred because it contains less water than traditional food coloring. Add the color gradually and whisk well, until you have the desired hue.
Ready to decorate
Scrape down the sides and bottom of the bowl thoroughly and whisk on high until the color is even. You may either decorate with the buttercream immediately, or chill it, covered in the fridge for up to two days. When ready to use, allow the buttercream to warm up a bit, then whisk it on high until the consistency is spreadable.