This is adapted from Jon, our chef teacher in Florence. Makes about 1-1/2 quarts.
4 cups whole milk
1/3 cup whipping cream
2/3 cup dark or bittersweet chocolate chips or bits (not semi-sweet; at least 50% cocoa)
1/2 cup cocoa powder
1/3 cup cornstarch
1 cup sugar
Use a wide deep pan. Place milk and cream in the pan and begin heating. Add chocolate chips and whisk until chocolate is melted.
Stir together cocoa powder, cornstarch, and sugar. Slowly add to the hot milk mixture and whisk constantly until your liquid thickens to a cream. Use a thermometer to keep the temperature between 140 and 176 degrees F. Be patient and stir till the mixture is as thick as melting ice cream. Pour the mixture into a container with a top and place in the fridge to get cold.
Pour the cold mixture into an ice cream/gelato maker and process according to the machine's directions, usually about 30 minutes. ** If it's still not thick enough, pour into a plastic container and freeze until firm. To serve, let stand 10 minutes before scooping.
**You may add small chopped candies, nuts, chocolate chips, etc in the last 5 minutes of processing.