Preheat your oven to 300°F (150°C) and line a cookie sheet with parchment paper.
In a large bowl, combine the egg whites and cream of tartar. Beat with a hand mixer or stand mixer on high until soft peaks form.
Gradually add the granulated sugar while continuing to beat until stiff peaks have formed. To check, lift the beater—if the meringue stands straight up without drooping, it’s ready. It’s crucial not to under-mix, as under-mixed meringue will result in cookies that spread too much.
Sift the hot cocoa mix over the meringue and carefully fold it in using a spatula. Be gentle—stirring too vigorously can cause the meringue to lose its volume.
Fold in the chocolate chips with a few gentle folds. The less you work the meringue, the better the cookies will set.
Using a 1 ½ tablespoon cookie scoop, scoop round mounds of batter onto the prepared cookie sheet, spacing the cookies 2 inches apart.
Sprinkle with chocolate sprinkles or mallow bits for added texture and flavor.
Bake in the preheated oven for 20-23 minutes, until the edges begin to brown slightly. Once you see the slight browning, turn off the oven and let the cookies sit inside for an additional 30 minutes. This helps them dry out completely.
Remove from the oven and place the cookies onto a sheet of wax paper to cool. Store the cookies in an airtight container at room temperature.