In your Instant Pot, add 4 ½ cups of water, 1 teaspoon Salt and 2 teaspoon Dry Mustard and give it a quick stir. Add pasta.
Set to Manual Mode for 5 minutes. It will take about 8 minutes to pressure up.
Once the Instant Pot and signaled the time is up, place a towel over the Quick Release valve and release the pressure. It will "spit" out water so the towel just helps to keep it from going all over your kitchen.
Open lid, and with a large spoon stir pasta. The pasta will clump up when cooking but quickly breaks apart when stirred.
Add Butter and Evaporated milk and give a quick stir.
Add Sharp Cheddar, Monterey Jack Cheese and stir to melt. Add Nutmeg. Add additional evaporate milk if you want it more creamy. Add salt and pepper to taste.
Serve and Enjoy! To Reheat, add additional milk or evaporate milk and heat in microwave.
Notes
Add some extra Ingredients to bulk up this family favorite recipe
1 Tbs Taco Seasoning for a Taco Mac
1 Cup cubed Ham and 1 Cup Frozen Peas
1 lb Cooked and crumbled Ground Beef with 1 Tbs Taco Seasoning