Salted Caramel Buttercream - December at Korrie's

This is the frosting on the cupcakes I made for the gift exchange--it's divine! It comes from this website: How to Eat a Cupcake. She also has a recipe for cupcakes, which I tried...twice! They fell miserably both times (let's just say I wasted a LOT of butter that day), so I ended up using a French Vanilla cake mix.

CARAMEL SWIRL BUTTERCREAM
MAKES ABOUT 2 CUPS (enough for about 12 cupcakes)

Caramel Drizzle
1 1/2 cups sugar
1 1/4 cups heavy cream
Pinch salt

Buttercream
3 large egg whites, at room temperature
3/4 cup sugar
Pinch salt
3/4 cup (1 1/2 sticks) unsalted butter, cut into pieces, at room temperature

For the frosting:
In a heavy-bottomed, high-sided saucepan, cook the sugar over medium-high heat until it begins to melt around the edges, about 5 minutes. Stirring with a clean wooden spoon, continue to cook until the sugar is melted and has turned golden amber, about 3 minutes longer.

Carefully pour the cream down the side of the pan in a slow, steady stream (it will bubble and spatter), stirring constantly until completely smooth. Stir in the salt. Pour the caramel into a small heatproof bowl and let cool completely before using. (The caramel can be stored in an airtight container in the refrigerator for up to 1 week; bring to room temperature before using.)

In a large, clean heatproof bowl, combine the egg whites and sugar. Set the bowl over (but not touching) simmering water in a saucepan and heat the mixture, whisking constantly, until the sugar has completely dissolved and the mixture is very warm to the touch (about 160°F on an instant-read thermometer), about 2 minutes (It always takes about 5 minutes for me). Remove the bowl from the saucepan. Using an electric mixer on high speed, beat the egg white mixture until it is fluffy, cooled to room temperature, and holds stiff peaks (the mixture should not look dry), about 6 minutes.

With the mixer on medium-low speed, add the salt and the butter, a few pieces at a time, beating well after each addition. If the frosting appears to separate or is very liquid after all the butter is added, continue to beat on high speed until it is smooth and creamy, 3-5 minutes more. Add the caramel drizzle (I only added about 1/2 cup) and beat until combined (or almost combined for a swirling effect), scraping down the sides of the bowl as needed.