Dissolve the cornstarch in 50ml whole milk, leave to rest.
In a small saucepan combine the heavy cream, the leftover milk, sugar, a pinch of salt, stir, bring to an almost boil, add the cornstarch milk and cook on medium constantly stirring until thickened. Take off heat, add the cream cheese, stir until smooth. Cool to room temperature, then transfer to the fridge overnight.
Freeze in your ice cream maker according to the manufacturer's instructions adding crushed Oreos at the last couple of minutes of churning. Store in an airtight container in the freezer or spoon right away.