Step 1

In the top of a double boiler, whisk egg whites and sugar until the mixture reads 140 on a digital thermometer.

Step 2

It is very important that the egg whites and sugar reach For one, it will cook the egg whites and prevent anyone from getting sick.  Second of all, it will melt the sugar and prevent the icing from being a grainy mess.

Step 3

Pour the egg white mixture into a mixer with a whisk attachment.  Whisk on medium-high speed until soft peaks form (when the egg whites do not move when the mixer is stopped).  It will also double in volume.

Step 4

While the whites are whisking, slice the butter into medium pieces and combine with shortening in a large bowl.  The butter should still keep it's shape.  Do not combine completely.

Step 5

Once soft peaks have formed, stop the mixer and add 1/4 of the butter/shortening mixture.

Step 6

Whisk on low speed for 15 seconds.  Stop the mixer and add another 1/4 of the butter/shortening.

Step 7

Whisk on medium speed for 15 seconds.  Stop the mixer and add the rest of the butter/shortening.

Step 8

Slowly increase the mixer speed from low to medium high, whisking at each speed for 10 seconds before increasing the speed.

Step 9

Continue to whisk on medium-high speed until the icing becomes fluffy and smooth.  Stop periodically to scrape the bowl.

Step 10

This is where Swiss Buttercream gets scary.  You've just taken something very heavy (cold butteand added it to something very light (whipped egg whites).  It is going to break and look ruined.  It's ok.  Just keep whipping until it comes back together and starts to get fluffy again.  It will happen.  I haven't had it not happen yet.

Step 11

Once the icing is fluffy, add the flavoring.

Step 12

Whisk on low for 45 seconds, then on medium for 45 seconds or until all of the vanilla is incorporated.

Step 13

Add the sifted confectioner's sugar (powdered sugar).  Whisk on medium until it is incorporated.

Step 14

More or less confectioner's sugar can be added, depending on the desired consistency.

Step 15

Once the icing is the consistency that you want, you can divide smaller portions into bowls and mix in food coloring.