My friend Nicole makes these around Christmas time and seriously, they are probably the very best cookie I have EVER had. They totally melt on your tongue- they're strange cause they're kind of fudgy but also kind of dry, but moist at the same time- I don't know how to describe it and it's been many months since I have had the pleasure. You definitely need a mixer for these, could not do them by hand. I don't have a KitchenAid but I bet it would come in handy for these. Also, Nicole says to splurge on the best quality of bittersweet chips you can find, says you can taste the difference. :-)
Chocolate Chiffon Fudge Cookies
3 cups
     bittersweet chocolate chips, divided 
6
     large egg whites, room temperature
4 ½
     cups confectioners’ sugar, divided
1 cup
     unsweetened cocoa powder
2
     tablespoons cornstarch
½
     teaspoon salt
Place
     2 cups chocolate chips in a microwave-safe container.  Melt chips in microwave, stirring
     every 30 seconds or so, for about 2 minutes or until no longer lumpy.  Set aside to cool slightly.
Using
     an electric mixer, beat the egg whites in a large bowl to soft peak
     stage.  This means that you fluff them up until it forms a peak when you pull the beaters out, but then they fold over on themselves.  Gradually beat in 2
     cups confectioners’ sugar. 
     Continue beating meringue mixture until it reaches stiff peak stage, which means when you pull the beaters out, they stay formed as peaked little mountains.
In a
     separate bowl, whisk 1 ½ cups confectioners’ sugar, cocoa, cornstarch, and
     salt.  On low speed, beat dry
     ingredients into meringue just until combined.  Stir in lukewarm chocolate and remaining cup chocolate
     chips.
Cover
     and chill dough for 1 hour (up to overnight).  Don’t skip this or your cookies will be flat.
Preheat
     oven to 350 degrees.  Line
     cookie sheets with parchment or slipat (do not skip with these cookies…
     they will stick)
Place
     remaining 1 cup confectioners’ sugar in bowl.  Roll 1 level tablespoon of dough into a ball; roll in
     sugar, coating thickly.  Place
     on prepared sheet.  Repeat
     with remaining dough, spacing 2 inches apart.  Bake until puffed and tops crack, about 10 minutes.
Cool
     on sheets on rack 10 minutes. 
     Transfer to rack to cool
Makes
     about 48 small cookies.

 
 


