Whisk together cornstarch, whipping cream, milk and sugar in a large saucepan over medium heat. Bring to a boil, then reduce heat and simmer until thickened and slightly reduced, about 30 minutes.
Meanwhile, puree mango chunks in a blender or food processor until smooth.
Stir mango puree into cream mixture and pour into individual cups. Cover each cup with aluminum foil and freeze until firm. Alternatively, freeze the kulfi mixture in a plastic-wrap-lined loaf pan and scoop it out with an ice cream scoop once frozen.
Notes
To use frozen mango: put the frozen mango chunks directly in the blender and carefully pour the warm (but cooled slightly) milk mixture over top and blend it together before freezing the Kulfi.Freezing time: Expect individual kulfi cups to take at least 4 hours in the freezer to become firm, 8 hours if using a loaf pan.