3 egg whites
4 ounces good quality white chocolate, coarsely chopped
1 cup sugar
1/4 cup water
3 sticks unsalted butter, room temperature
1. Bring a small pot of water to a simmer over medium heat.
2. Place egg whites in bowl of stand mixer and attach whisk.
3. Melt white chocolate in heat-proof bowl over simmering water. When chocolate is almost completely melted, remove from heat. Stir until all chocolate is melted, set aside.
4. Combine sugar and water in a small saucepan. Heat over medium heat and stir until sugar is dissolved. Bring mixture to a boil without stirring, until the temperature reaches 238 F.
5. Start whipping the egg whites on medium-low speed. Slowly pour boiling sugar into the egg white mixture, being careful not to get the sugar on the whisk attachment. Continue to whip until the mixture has cooled and a stiff meringue has formed.
6. Add butter, 2 tablespoons at a time. When all of the butter has been added, raise speed to medium and beat until the mixture has appeared to curdle. Continue to beat, and the buttercream will come together. At this point, add the melted chocolate and beat until well-combined.
Frost or pipe buttercream onto cooled cupcakes. Recipe from Sky High.