Fortunately I had the developer of the recipe just a few feet away. Apparently, to measure out egg whites, you have to whisk them first. Breaking them up is the only way to separate the whites out enough to measure them. Whisk too much and you'll start to froth the, so just a quick hit with a fork or whisk will do the job. Maybe this is common sense, but it was news to me.
Also, you should totally make the Chocolate Tacos with Ice Cream and Peanuts. It received our highest rating in the magazine and was a Staff Rave in May. It also calls for 1 tablespoon egg whites, which is key to getting the right texture in the shells.