2In mixer fitted with the whisk attachment, beat your egg whites and salt on medium speed until frothy about 1 minute and with machine on high speed, gradually add your sugar and add your cream of tartar, vanilla extract and espresso powder after the sugar is all finished. The mixture should be thick and holds stiff peaks, about 5 minutes. Fold in chocolate chips. Drop by heaping tablespoons onto prepared baking sheet, apace them 2 inches apart. Bake for 30 minutes then rotate the pan and bake for another 30 minutes. Turn off the oven and allow meringues to cool while in the oven about 2 hours. Yes, you must do this. Remove and store in airtight container only up to 4 days.