Pour the milk into a medium-sized, heavy saucepan. Bring to a low simmer over medium-high heat.
Remove from heat.
In a metal bowl, whisk together the eggs yolks, sugar and corn syrup until blended.
Form a kitchen towel into a ring and place the bowl on top to prevent it from moving. Or use a bowl with a no slip bottom.
Gradually pour the hot milk into the yolk mixture, whisking constantly.
Return the mixture to the same saucepan and place over medium-low heat.
Cook, stirring slowly and continuously with a wooden spatula, until the custard thickens and leaves a path on the back of the spatula when a finger is drawn across it, about 6 minutes, do not allow to boil.
Pour the custard through a medium-mesh sieve set over a clean metal bowl.
Add the chocolate and cocoa and stir until the chocolate melts.
Refrigerate until cold, about 1 hour.
Transfer the custard to an ice cream maker and process according to the manufacturer's instructions.
Or place the gelato in a freezer container and freeze.