Freeze your ice cream maker's canister if required by manufacturer's instructions.
In a small bowl mix 2 tablespoons of milk with cornstarch to make a slurry. Set aside.
In a medium bowl, combine the cream cheese and salt. Use a hand mixer to beat until smooth and combined. Set aside.
Combine the remaining milk, cream, sugar, corn syrup and vanilla seeds into a large saucepan. Bring to a rolling boil over medium high heat; boil for 4 minutes. Remove from heat and whisk in the cornstarch mixture. Return to the pan to the heat and bring to a boil, whisking constantly until mixture thickens, about 1-2 minutes.
With hand mixer on medium speed, add the cream mixture in a steady stream until combined.
Mash bananas (by hand for a chunkier mix - or in a blender for a smoother texture) and add banana puree to the cream mixture. Stir well to combine. Cover with plastic wrap and refrigerate until well chilled, at least two hours or overnight.
Transfer the custard to the ice cream canister and churn the ice cream according to manufacturer's instructions.
While ice cream is churning, heat the Peanut Butter Magic Shell until liquified, but not hot... Usually one to two 20-second bursts in the microwave, stirring in between will do it.
When ice cream is done, alternate spooning ice cream with peanut butter magic shell into a container, so that there are chunks and swirls of peanut butter throughout the ice cream. Freeze ice cream for at least 4 hours or until firm. Serve.