In the Instant Pot, combine dried macaroni, water, and salt.
Place the lid on the Instant Pot, and close by twisting in place. Close the valve. Set the Instant Pot to High Pressure at 4 minutes (The Instant Pot will take about 12 minutes to come pressure.).
Once the Instant Pot finishes cooking after the 4 minutes, open the valve using something to protect your hands as the steam will be hot. Turn Instant Pot off. After the Instant Pot has released all its pressure, untwist the lid, and pull the lid off away from you. Drain any remaining water.
Stir in the milk, and butter. Once the butter has melted, and the milk has been mixed completely, add in the cheddar, and the mozzarella by one handful at a time to make a creamy sauce.
Once you have added one handful, mixed until the cheese has been completely melted. Then add another handful of cheese. Continue until all cheese has been added, and all cheese is melted in the macaroni.
Serve your Instant Pot macaroni and cheese immediately, or you can set the Instant Pot to the “warm” setting.
Notes
Use enough water: This recipe calls for 4 cups of water. Don't put any less otherwise your pasta may get the Burn Notice.Make sure water covers the pasta: You want your water to fully cover your pasta noodles.