To accompany my mex fest, I made gelato with Mexican chocolate. In short, Mexican chocolate is "toasted very dark...then coarsely ground over heat with sugar (and often cinnamon, almonds, and vanilla)...making a disc that more or less dissolves in milk or water, to drink" - Rick Bayless
It's my favorite hot chocolate. To make it properly, you pour hot milk over the chopped chocolate in a blender, then blend to create a thick foam. Yum yum.
As a starting point, I referenced this excellent gelato posting on The Traveler's Lunchbox. As described in this posting, the main difference between gelato and ice cream is that gelato uses only milk, not cream. This means a more intense flavor because the fat is a "flavor-blocker". You may be familiar with this principle with chocolate - e.g. hot chocolate made with water instead of milk is more intense and dissolving cocoa powder in hot water before adding to cake batter will create a more intense chocolate flavor. I digress.
So I adapted the Chocolate Gelato No. 2 on The Traveler's Lunchbox (adapted from an epicurious recipe) by substituting Mexican chocolate for the bittersweet chocolate and reducing the cocoa powder to 1/2 cup. This resulted in a hyper-chocolatey gelato that about knocked me out. I can't imagine what would happen with a full cup of cocoa. It was well-liked by all but with all this chocolatey goodness, the Mexican chocolate subtleties were practically obliterated.
So I tried again, this time eliminating the cocoa powder and got the result I wanted, basically the flavor of Mexican hot chocolate turned into a creamy, cold dessert (recipe below). It was also vaguely reminiscent of the famous Frrrozen Hot Chocolate at Serendipity3 in Manhatten (you must go if you're in town - it lives up to the hype).
Despite this, I was not completely satisfied with the texture. It was a little grainy/icy, not creamy enough. Next time I might try adding a tiny bit of vodka, recommended by a Cook's Illustrated sherbet recipe to create a smoother, more refined texture. Also, I might play around with the milk/sugar ratio. The CI recipe mentions that "...sugar makes it harder for water molecules to form ice crystals and thus lowers the freezing temperature of the mixture...sugar also reduces the size of the ice crystals, physically interfering with their growth. Smaller ice crystals translate into a less grainy texture."
Lastly, the TL recipe says to bring the custard to 160F and the epicurious one says 170F. Most of my ice cream recipes recommend at least 180F, which proved exactly right. If you don't get it to custard texture, there's no point in freezing the stuff.
Here's my final Mexican chocolate gelato recipe, adapted from The Traveler's Lunchbox:
1 1/2 cups whole milk
1 cup evaporated milk (whole milk is ok, too)
3/4 cup granulated sugar
4 large egg yolks
Have ready a large bowl of ice and cold water (to cool mix after cooking). Coarsely chop chocolate. In a 2-quart heavy saucepan bring milk, evaporated milk, and about half of sugar just to a simmer, stirring until sugar is dissolved. Remove pan from heat and add cocoa powder and chocolate, whisking until chocolate is melted and mixture is smooth. In a bowl with an electric mixer beat yolks, remaining sugar and salt until thick and pale. Add hot chocolate mixture in a very slow stream, whisking, being careful not to cook the eggs. Then pour the mixture back into saucepan. Cook custard over moderately low heat, stirring constantly, until a thermometer registers 180°F (don't let it boil - it will cook the eggs, yuck!). Pour custard through a sieve into a metal bowl set in ice and cold water and cool. Chill custard, covered, until cold. Freeze custard in an ice-cream maker. Transfer to an airtight container and put in freezer to harden for several hours.