500 grams white sugar
3/4 cup water
8 egg whites at room temperature
1 pound salted butter
1 pound unsalted butter
1/2 teaspoon cream of tartar
Best made with a stand mixer!!!
Combine sugar and water in a small saucepan and boil rapidly until it reaches 248 degrees on a candy thermometer. Meanwhile whip egg whites on medium until they start to break up. Add Cream of Tartar and continue whipping on high until they are stiff. This usually is the same length of time as it will take for the sugar and water to reach 248 degrees.
Once the sugar syrup is at temperature, slowly and very carefully (it is dangerously hot) pour into the whipped egg whites in one slow steady stream. Try not to let it hit the whisk as it will spray crystals onto the edge of the bowl which you dont want because if they get in your piping bag it can gum up your tip.
Whip the egg whites until the bowl is completely cool to the touch. This can take 20 to 30 minutes.
Change whisk to paddle attachment as this will help avoid air bubbles in your frosting.
Gradually add all the butter a tablespoon or so at a time until it is fully incorporated. Now this is where the miracle happens! The egg whites will lose their volume and will go though lots of different consistencies. They can go back to a liquid, they can look like they are curdled or like cottage cheese. But have faith! Keep mixing and it will all come together. Then add your vanilla or favouring of choice.
This buttercream is very sensitive to temperature but it will turn out to be the most beautiful of all frostings that you have tried.