Heat a large saucepan over medium heat and add 2 1/2 cups of milk. Whisk in the sugar, salt and cocoa powder until dissolved and combined. Keep it over low heat, stirring often for a minute or two.
In a bowl, whisk together the remaining 1/2 cup milk and cornstarch until smooth. Slowly whisk it into the warmed milk mixture and increase the heat to medium. Whisking the entire time (especially the bottom), bring the mixture to a boil. Cook it for 2 to 3 minutes until it has slightly thickened. Remove the pan from the heat.
Heat the heavy cream just until bubbles appear around the edges. Place the chopped chocolate in a bowl and pour the cream over top. Let it sit for 1 minute. Stir until a thick and smooth ganache forms and all the chocolate has melted. Stir the ganache into the milk mixture. Transfer the entire thing to a bowl let it chill in the fridge until completely cold, a few hours.
Once cold, pour the mixture into your ice cream maker and churn according to the directions. I use the kitchenaid attachment and churn for 25 minutes. After 22ish minutes (or a minute or so before finishing), drizzle in 1/2 cup of the peanut butter. Finish churning and remove the bowl. Stir in the remaining peanut butter (I love huge chunks!) and the HELLO pretzel bites. Place in a freezer safe dish or container. Freeze for 4 to 6 hours before serving.