Place oven rack in the center of the oven, preheat the oven to 300 deg. some have used 250. line baking sheet with parchment paper, set to the side.
In a stand mixer fitted with the whisk attachment, beat the egg white and salt until frothy this will take about 1 minute
With the machine on medium-high speed gradually add the sugar about 1 tablespoon at a time, add the cream of tarter, vanilla and espresso powder. Increase speed to high and beat until the mixture is thick and holds a stiff peak this will take between 3-5 minutes.
Using a spatula fold in the chocolate chips then drop 1/4 - 1/2 cup ( I used a large spoon) of the mixture onto the prepared sheet about 2 inches apart. bake for 30 minutes
Rotate the pan and bake for another 30 minutes, turn oven off and allow the meringues to cool completely while still in the oven this will take about 2 hours. store in airtight container.
my research shows a few changes to this receipe. some cook it at 400 for 40 minutes, but most complain they burn after 30 min. some cook it at 250. I also noted a lot of these call for instant espresso powder I did not and have seen others that do not call for the instant, the other day I used Starbucks brand expresso in my brownies I will have to look at the bag in the store to see if it was instant or not but I do not think it was, I will get back to you on that matter, I am beginning to wonder if all espressos are in fact instant. You can even add cocoa powder & chips, lastly i have seen regular sugar replaced with powdered