Measure milk then remove about five tablespoons to a separate small bowl and mix in the corn starch and set aside.
In a medium sauce pan off the heat combine the sugar with the cocoa powder whisking to remove any lumps then add the rest of the milk, heavy cream, dry milk, and salt.
Heat over medium high heat whisking to dissolve everything until it comes to a boil. Reduce heat to medium and continue stirring for four minutes. After four minutes stir up the reserved milk with corn starch and add to pot with the rest of ingredients. Heat for another minute to let cornstarch thicken the ice cream base.
To get extra creamy ice cream use an immersion blender for a few seconds. Pour ice cream base into a container with lid or bowl and cover with plastic wrap then chill over night.
When ready to make ice cream add mint extract and pour into ice cream machine and churn according to manufacturers directions. When the ice cream is finished stir in the brownie pieces and junior mints. Store in freezer safe containers and let freeze at least four hours.