In a small bowl, whisk together 2 tablespoons of the milk with the cornstarch; set aside. In a medium bowl, whisk together the peanut butter and salt; set aside.
Combine the remaining milk with the heavy cream and sugar in a medium saucepan and place over medium heat. Cook, stirring occasionally, until the sugar dissolves, about 3 minutes. Remove from the heat & gradually whisk in the cornstarch mixture. Return to medium-high heat and bring to a boil; cook until the mixture is slightly thickened, about 1 minute. Gradually pour into the bowl with the peanut butter and whisk until smooth. Set the bowl in the ice water bath until cool, about 20 minutes, whisking occasionally. Cover and refrigerate until well chilled, at least 4 hours or overnight.
Pour the ice cream base into an ice cream maker and churn according to the manufacturers directions. Spoon a small layer of jam into a freezer-safe container & lightly spoon a layer of ice cream on top. Continue to alternate layers of jam and ice cream until container is full. Freeze until firm, at least 4 hours.