Step 1

Set two oven racks in the middle positions and preheat the oven to 350°F. Line two baking sheets with parchment paper.

Step 2

Break the chocolate into small pieces into a microwave-safe bowl. Microwave in 20-second intervals, stirring in between each bout of heat, until about 75% melted. Stir until smooth, allowing the residual heat in the bowl to melt the chocolate completely. (This technique ensures the chocolate mixture will not get too hot and scorch.) Set aside.

Step 3

In a large bowl, beat the egg whites with the cream of tartar, vanilla and salt until soft peaks form when you lift the beaters (the peaks should be just starting to hold, and will melt back into themselves after a second). Gradually add the sugar, continuing to beat until stiff peaks form (the peaks will stand straight up when the beaters are lifted from the mixture). Pour the warm chocolate and chocolate chips into the bowl and fold with a spatula until the batter is uniform. Do not overmix.

Step 4

Immediately drop heaping tablespoons of the batter about 1 inch apart on the prepared baking sheets. Bake for 8-10 minutes, or until the cookies look dry on the surface but are still very gooey inside when you press on them. Let the cookies cool for a few minutes on the baking sheets, and then transfer to a rack to cool completely. Enjoy on the same day or carefully wrap in an airtight container (don't stack them as they crumble easily).