1 3/4 cups milk
1 3/4 cups cream
4 tablespoons cornstarch
2/3 cup sugar
2 teaspoons unsweetened cocoa powder
3 tablespoon instant-coffee granules or espresso granules
2 teaspoons vanilla
Special equipment: an ice-cream maker
Stir together 1/2 cup milk and cornstarch.
Whisk together sugar, cocoa, cream and remaining 1 1/4 cups milk in a small heavy saucepan and bring to a boil over moderate heat, stirring.
Whisk in coffee granules.
Stir cornstarch mixture again and whisk into coffee mixture. Return to a boil, whisking, then remove from heat.
Add vanilla to saucepan, stirring.
Set saucepan in a large bowl of ice water to cool, whisking frequently.
Freeze coffee mixture in ice-cream maker.
Transfer to an airtight container and store in freezer.