Freeze ice cream bowl according to manufacturer's directions but you shouldn't be able to hear any liquid splashing around inside.
In medium saucepan over medium heat, whisk dry ingredients (sugar, cornstarch and salt) together for 1 minute.
Add 1 ⅔ cup of whole milk. Continuously stirring over medium heat as the contents of the pan thicken ( should take about 5 minutes). Heat for an additional minute at a low boil, stirring the whole time.
Meanwhile, in a measuring cup combine the remaining cup of milk, heavy cream, whiskey and vanilla.
After the six minutes are up and the base is thickened, turn off the heat and add the remaining milk/whiskey mixture to the pan.
Pour contents of pan into a wide, shallow glass bowl and cover with plastic wrap. Store in refrigerator until the base reaches 42° temp. This should take about 2 hours. You can also set the bowl over a pan or sink filled with ice if you're in a hurry. But make sure you stir the base before taking the temp of the contents as the center could still be warm. Don't rush this step!
Pour chilled base into prepared ice cream maker and process according to manufacturer's directions. My ice cream maker takes approximately 25-30 minutes to thicken.
During the last five minutes of processing and with the machine running, slowly pour melted chocolate into ice cream base.
Remove the paddle from container and spoon ice cream base into the bottom of long rectangular freezer-safe container (needs a lid).
Cover the container and freeze for about 6 hours till firm.
Remove from the freezer about 10 minutes before serving.