Combine the cream cheese and salt in a bowl and whisk until creamy, about two minutes.
Fill a large bowl with iced water and have a gallon zip lock bag ready.
Place the milk into a small pot.
Take 2 tablespoons of the milk out and add that to the cornstarch and mix until it dissolves. Set aside.
Add the cream, sugar, corn syrup and vanilla to the milk and bring to a rolling boil.
Boil for 4 minutes on medium and then take off the heat.
Add the cornstarch mixture and whisk until well mixed in.
Place the pot back on the heat and simmer for a further 2-3 minutes and the mixture gets slightly thicker. Remove from the heat.
Add half of the chopped chocolate bar and let it melt in the mixture.
Slowly add the mixture to the cream cheese whisking as you add it. Don't add too much at one time or lumps will be harder to get out.
Once the mixture has all been added to the cream cheese our it into the zip lock bag and seal closed.
Place the bag into the iced water and let it cool for about 30-40 minutes.
Once the custard is cool, add it to your ice cream machine and follow the makers instructions. it should take about 30 minutes depending on how cool it is.
Once the ice cream is fully churned take the beater out of the canister and add the peanut butter,crushed pretzels and rest of the chocolate.
Use a wooden spoon to swirl all of the ingredients through the ice cream.
Cover the surface with a piece of parchment paper and store in the freezer overnight or at least 4 hours.