Combine milk, cream, corn syrup, sugar, salt and chocolate in a large saucepan. Cook over medium heat, stirring frequently, until milk is steaming and chocolate is mostly melted. Beat egg yolks with a wire whisk until light in color. Add about 1 cup of the hot mixture to the egg yolks and mix well. Add mixture back into pan. Stirring frequently, cook until custard coats the back of a spoon or temperature is about 180°F. Do NOT boil. Remove from heat and add vanilla extract.
Transfer mixture to a shallow bowl; cover and refrigerate for at least 8 hours or overnight.
Whisk the chilled custard and pour into ice cream maker or gelato machine. Make according to manufacturer's suggestions. The gelato is ready when it is the consistency of soft serve ice cream or about 15 minutes. Serve immediately or pour into container and freeze until ready to serve.
Recipe Note - placing custard in a container with a spout makes it easier to pour into the machine.