For the chocolate sauce in a small saucepan over medium heat combine 80ml water, 45gr sugar, cocoa powder, cook 2min stirring until uniform. Add the chopped dark chocolate, cook until completely melted and glossy.
Dissolve the cornstarch in 50ml whole milk, leave to rest.
For the ice cream in another small saucepan over medium heat combine the heavy cream, the leftover milk, 85gr sugar, a pinch salt, stir, bring to an almost boil, add the cornstarch milk and cook constantly stirring until thickened. Take off heat, add the cream cheese and the chocolate sauce, stir until smooth and combined. Cool to room temperature, then transfer into the fridge overnight.
Freeze in your ice cream maker according to the manufacturer's instructions adding 65gr chopped KitKat Dark candy at the last couple of minutes of churning. Store in an airtight container or spoon right away.