Cream Cheese Swiss Meringue Buttercream Frosting (what a mouthful!)

Why I Love This Recipe
I had just discovered SMBC recently, but wanted to make a cream cheese frosting for red velvet cupcakes. "Maybe," I thought, "Just maybe this exists!" The internet said yes, but all of the recipes gave annoying weight measurements instead of simple volumes. Since I don't own a food scale I converted this to imperial measurements. The ratio may be slightly off of the original recipe but I guarantee it works. This frosting is delicious and so light you won't believe you are scooping such a vast amount of butter into your mouth with such ease. Don't be afraid of this seemingly complicated frosting - it's WAY easier than you think!
Ingredients You'll Need
4 egg whites
3/4 c sugar (regular granulated white sugar, not powdered!)
1 c butter (two sticks) at room temperature
1 c cream cheese (two 8-oz packages) at room temperature
1 t vanilla extract
1/4 t lemon extract (optional but highly recommended - it adds a lightness to the otherwise heavy frosting)
Directions
If you have a Kitchenaid mixer, this recipe is easy. If you've got a handheld, it will be a bit more difficult but still do-able with strong arms. If you only have a whisk, please don't try this! The amount of beating required is just too much to do entirely by hand.
Find a heat-safe bowl that will dip down into a saucepan without touching the bottom. If you have it, the Kitchenaid bowl fits perfectly into the 1L Visions(r) glass saucepan. You are basically creating a double-boiler, so if you have one of those you could use it. I prefer to just use the Kitchenaid bowl in the pan as it means one less thing to wash.
Fill the saucepan with enough water so that the bottom of the bowl is immersed.
Mix the egg whites and sugar together in the bowl or double boiler. It will look gross.
Turn the heat to medium-low and stir occasionally.
In the beginning you can stir every couple minutes, but as the water heats up it requires more stirring so that the egg does not cook to the sides.
Most recipes ask you to cook this mixture to 140 degrees.
I do not have a candy thermometer, so I use the following method: dip your thumb and forefinger into the mixture, remove them, and rub together. If it feels gritty it's not ready. If it feels smooth & sticky it is done.
Transfer the mixture to a mixing bowl if using a double boiler. If using the Kitchenaid bowl-in-a-pot method, just remove the bowl and hook it up to the mixer!
Using the whisk attachment, whisk the mixture until it forms "stiff glossy peaks" and feels no warmer than body temperature.
If it is hot enough to melt butter let it go for a few more minutes.
This usually involves about 10-15 minutes of mixing (see why hand-whisking would be terrible?)
Start adding the butter to the meringue in tablespoon sized chunks.
Wait until each chunk is incorporated before adding the next.
After all the butter is added, add the cream cheese in the same way.
Many people report their frosting "breaking" and turning into disgusting clumps and watery goo. If this happens, DON'T PANIC, and keep the mixer going. Everything will eventually coalesce back into meringue texture.
Turn the mixture up to high again and beat until smooth (can take up to 10 minutes)
Add the flavourings at the very end and beat to incorporate.
This frosting does not chill well so don't plan on making it ahead of time for later use. If you must do it this way, you will need to re-beat it in order to regain good consistency. Note that I have not been able to do this with much success.