Le Dauphin au Chocolat (Cocoa flavored Semi-freddo)

This recipe is for my dear (and occasionally patient) friend, Lis, who has been bugging me to post it on my blog ever since I made it for her more than a year ago. Well, next week is her anniversary, so I intend to count this as her present. Now, if she's really nice to me, maybe I'll even make it for her.
You'll notice in the title that this recipe says "semi-freddo". Not ice cream, not gelato. This is a completely different item, and if you're Jonesing for a serious chocolate hit, then this will almost certainly do the trick.
Semi-freddo, in Italian, means half-cold, or more loosely translated, half-frozen. In this case, that's the perfect name for this sweet. The semi-freddo will not freeze up hard. The massive amount of sugar prevents it from doing so, or even from forming large ice crystals. The result is therefore a smooth, velvety chocolate ice cream that’s better (and far, far richer) than any soft-serve ice cream you’ve ever dreamed of.
My wife loves this stuff, but she can't eat more than about a quarter cup at a time, so it lasts a looong time on our house. It's so rich that most people can't eat a lot at once, so don't stress that your final product doesn't make buckets and buckets of the stuff. Even the amount in this recipe is enough to last awhile.

INGREDIENTS:

5 Large Egg Whites (or 6 medium)
1½ cups Superfine Sugar
¼ t. Cream of Tartar
½ cup Unsweetened Cocoa
1 cup Heavy Cream
½ cup Powdered Sugar
1 t. Vanilla Extract

PREPARATION:

1. Place the Egg Whites and Sugar in a large mixing bowl and place over a large pan of boiling water. Don’t let the mixing bowl touch the boiling water.
2. Stir continually with a whisk until the mixture is warm, but not hot. Remove form the heat.
3. Add the Cream of Tartar, and beat with the whisk attachment of your mixer until the meringue is stiff, white, and shiny.
4. In a large, chilled mixing bowl, beat the Heavy Cream and Powdered Sugar until soft, gentle mounds form when you lift out the beaters. Add in the Vanilla just at the end and beat for 30 more seconds.
5. Using a large whisk, or a clean spatula, fold the meringue into the cream until completely incorporated.
6. Pour the mixture into a large, fancy serving dish, or individual fluted glasses, and cover with Saran Wrap.
7. Freeze for at least 4 hours, or up to 5 days, before serving.