Place an oven rack in the center of the oven and preheat the oven to 300 degrees F. Line a baking sheet with parchment paper. Set aside.

In a stand mixer fitted with the whisk attachment, beat the egg whites and salt on medium-low speed until frothy, about 1 minute. With the machine on medium-high speed, gradually add the sugar, about 1 tablespoon at a time. Add the cream of tartar, vanilla extract and espresso powder. Increase the speed to high and beat until the mixture is thick and holds stiff peaks, 3 to 5 minutes. Using a spatula, fold in the chocolate chips.

Drop 1/4 to 1/2 cupfuls of the mixture onto the prepared baking sheet, spacing them 2 inches apart. Bake for 30 minutes. Rotate the pan and bake for another 30 minutes. Turn off the oven and allow the meringues to cool while still in the oven, about 2 hours.

Remove from the oven and let cool completely. Store in bags or an airtight container up to 4 days.

Photograph by Gemma Comas