Add the dry macaroni, cornstarch, and salt to a deep microwave-safe bowl. Stir to coat the pasta and then stir in the water.
Microwave for 2 minutes, stir well, then microwave for another 2 minutes.
Stir in 1-2 tablespoons of water, as needed. Continue to heat in 2-minute intervals and add 1-2 tablespoons of water with each heating, as needed. Total cooking time will be 6-8 minutes but will depend on your microwave and the brand of pasta you use.
When the pasta is soft, stir in the milk and shredded cheese until combined.
Microwave in 30 second intervals until the cheese is melted.
Let stand for 1 minute before serving.
Notes: The bowl will be extremely hot. Be sure to use oven mitts when handling the bowl. You can reduce or increase the cheese to your desired level of cheesiness.