4 egg whites
1 cup sugar
Pinch of cream of tartar
1 tsp vanilla extract
Set up a double boiler. When the water is simmering, add egg whites and sugar and whisk until the sugar has dissolved, about 4 minutes, and the mixture registers about 160˚ on a candy thermometer, or the sugar is completely dissolved and the mixture looks frothy. Transfer the egg whites to the bowl of a stand mixer fit with the whisk attachment and add the cream of tartar. Whip on high for 3 minutes, then add in vanilla extract. Continue to whip (about 3 minutes more) for a total of 5-7 minutes, or until the mix starts to become stiff and glossy. You’ll know the mixture is ready when it will hold a stiff peak without deflating.
Transfer the frosting to a piping bag (or sturdy plastic bag) and start frosting the cupcake from the outer edge inward. You want to build a sturdy coil, overlapping in a concentric circle as you make your way up.
Let frosted cupcakes chill in the refrigerator for at least 30 minutes while you make your chocolate coating. The frosting should not be sticky when you dip them; it should feel dry and firm to the touch.