In a small saucepan, bring the sugar and 2/3 cup water to a boil. Boil until the syrup reaches the soft-ball stage (238 degrees on a candy thermometer).Advertisement
Meanwhile, in the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites on low speed until foamy. Add the cream of tartar; beat on medium-high until stiff but not dry.
With the mixer running, slowly pour the hot sugar syrup into the egg whites, and beat on high speed until mixture has cooled, about 15 minutes. Add food coloring to tint. Be careful not to overbeat. Use immediately.
Make each batch of this coating as needed; do not double the recipe.