Don't be fooled — even though it's frozen, this dessert packs some heat. Serve à la mode to mellow out the fire. If you can't find Mexican chocolate (such as Ibarra), adding equal parts cinnamon and cayenne pepper to regular baking chocolate is a good substitute.
Place the chocolate in a bowl and set it on top of a pot filled with just enough water to touch the bottom of the bowl. The bowl should be large enough to sit partially in the pot without touching the bottom. Put the pot on low heat to melt the chocolate slowly. Stir with a spatula occasionally to ensure even melting. Once it is completely melted, remove from heat, but leave the bowl on top of the pot. Fold in the cinnamon and cayenne.
Meanwhile, pour the heavy cream into a bowl, and set over a larger bowl filled with ice and a small amount of water. Beat with a whisk until it forms soft peaks. Place in the refrigerator.
Now, in another bowl, beat the egg whites with a whisk until they form soft peaks. You can also use an electric mixer to speed the process. Slowly stream in the sugar a little at a time, continuing to beat the eggs. Stop when the whites have formed hard peaks.
Gradually fold in the egg whites into the melted chocolate. Once they are folded in, gradually fold in the whipped cream. Make sure to scrape the bowl each time.
Now, pour the mixture into a baking dish and freeze for at least 3 hours.
Serve with vanilla ice cream. If it is too hard to serve, leave out at room temperature for about 10 minutes.