Take 3 tablespoons of the whole milk and mix with the cornstarch in a small bowl. Set aside.
In a medium-large saucepan (4 quart) over medium-high heat, heat the rest of the whole milk, heavy cream, evaporated milk, sugar, and corn syrup. Keep a close eye on this as you do not want it to boil over or burn.
When it comes to a tame boil, whisk in the cocoa powder. Cook at a moderate boil for approximately 4 minutes. After 4 minutes, give your cornstarch slurry a quick stir to make sure it is still blended. Whisk this slurry into the milk mixture and cook for another minute, stirring with a spatula until thickened.
Remove from heat. Stir in chopped chocolate and salt. Keep stirring until smooth and chocolate is melted. Stir in vanilla.
Transfer the mixture to a large shallow bowl. Submerge bowl in a larger bowl full of ice water. (I actually used the sink). Leave in the ice bath for 30 minutes, stirring frequently, until completely cooled. You could also put it in the fridge overnight.
Pour mixture into ice cream maker and churn according to ice cream maker directions. (I churned for 25 minutes total.) Add in cocoa nibs for last five minutes of churning.
Move to freezer and freeze until solid. Mine needed to be frozen overnight to achieve a firm texture.