Dissolve the cornstarch in 50ml whole milk, leave to rest.
In a small saucepan over medium heat combine the heavy cream, the leftover milk, sugar, a pinch of salt, 2-3tbsp malted milk powder, stir, bring to an almost boil, add the cornstarch milk and cook constantly stirring until thickened. Take off heat, add the cream cheese, stir until fully incorporated. Chill to room temperature, then transfer into the fridge overnight.
Freeze in your ice cream maker according to the manufacturer's instructions adding the chopped original KitKat candy at the last couple of minutes of churning. Transfer into an airtight container and store in the freezer or spoon right away.