1. Adjust oven racks to upper- and lower-middle positions and heat oven to 200 degrees. Line 2 large baking sheets with parchment paper.
2. With electric mixer, beat egg whites at medium-low speed until opaque and frothy, about 30 seconds. Add cream of tartar, increase speed to medium-high, and, watching carefully, beat egg whites until white, thick, voluminous, and consistency of shaving cream (see photo below), about 90 seconds. Slowly sprinkle in half of sugar and continue to beat until incorporated, about 60 seconds. Add vanilla. Reduce speed to lowest possible setting, sprinkle in remaining sugar, and mix just until incorporated.
3. Fold chocolate chips into the meringue.
4. Following illustration below, use 2 soupspoons to place dollops of meringue, 2 tablespoons each (about size of walnut), 1 inch apart, fitting 3 rows of 5 cookies on each sheet. Bake for 1 1/2 hours or until cookies have smooth, dry, and firm exteriors. Turn oven off and allow cookies to cool in oven for several hours. Once cool, store cookies in an airtight container, where they will keep for up to 2 weeks.
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