In a small bowl or measuring cup, whisk together 2 tablespoons milk with the cornstarch to make a slurry and set aside.
In a medium mixing bowl, stir together the mascarpone, cinnamon, and salt. Set aside.
In a medium saucepan, heat the remaining milk, cream, sugar, corn syrup, and vanilla bean seeds. Heat over medium-high and bring to a boil for about 4 minutes. Remove from the heat.
Meanwhile, practically fill a large mixing bowl with ice and water to create an ice bath. Set aside.
Slowly temper in a small amount of the hot cream into the cornstarch mixture. Add everything back to the saucepan and whisk to combine. Place the saucepan back over medium-high heat, stirring constantly, and bring back to a boil for about a minutes, or until slightly thickened.
Remove from the heat and gradually whisk the cream mixture into the mascarpone mixture. Place the bowl over into the ice bath and refrigerate until cold. Mean while, make the blackberry sauce (recipe to follow).
Once cold, pour into an ice cream machine and churn the ice cream according to the manufacturer’s directions.
Once done, pack and layer in the ice cream with the blackberry sauce into a loaf pan or other freezer-safe container. Cover with a piece of wax paper and freeze until solid.