1cup semi-sweet chocolate chips, divided
1 1/2cups powdered sugar, divided
1/3cup unsweetened cocoa powder
2tsp arrowroot powder, or corn starch
2 egg whites, room temperature
1/2tsp vanilla extract
1/8tsp cream of tartar
Position 1 rack in top third and 1 rack in bottom third of oven and preheat to 350°F.
Lightly spray two cookie sheets with non-stick spray.
Place 1/2 cup chocolate chips in small microwave-safe bowl. Cook in 15-second intervals until chocolate softens; stir until melted and smooth. Cool chocolate to lukewarm, about 10 minutes.
In a separate bowl, whisk 1/2 cup sugar, cocoa, and arrowroot powder (cornstarch) in small bowl to blend.Using electric mixer, beat room-temperature egg whites, vanilla, salt, and cream of tartar in medium bowl until soft peaks form. Add remaining 1 cup sugar in 4 additions, beating just to blend after each addition. Continue to beat until meringue is thick and glossy like marshmallow creme, about 2 minutes longer.
Beat in cocoa mixture. Fold in melted chocolate, then 1/2 cup chips.
Drop batter by rounded tablespoonfuls onto prepared sheets, spacing 3 inches apart. Bake cookies 7 minutes. Reverse sheets and bake until dry-looking and cracked, about 6 minutes. Cool cookies on sheets 5 minutes and move to cooling rack to dry completely.
*Tip* These cookies are best eaten the day they're made or they will become too crumbly. When storing, store in an air-tight container.