Add pasta to the inner pot of the pressure cooker.
Add enough water cover pasta by 1 inch. Depending on the shape of the pasta, it usually takes 3-5 cups of water.
Lock lid in place, and turn pressure release valve to SEALING.
Cook on MANUAL/HIGH pressure for 4 minutes.
Carefully turn pressure release valve to VENTING.
Unlock lid, and drain pasta.
Return pasta to inner pot.
Add milk, salt, pepper, and mustard.
Stir to combine.
Press CANCEL.
Stir in cheese, and continue stirring until cheese has melted and is combined.
Notes
Pasta: I like to use small shell pasta. If you use another type of pasta, you may find that you need to adjust the cooking time.
Evaporated milk: You can use regular, low-fat, or fat-free.
Mustard: I like to use Dijon, but if you don't have Dijon mustard, dry mustard makes a good substitute. I use about ¼-1/2 teaspoon or so if I'm using dry mustard.
Cheese: I use an aged white cheddar when I make this mac and cheese. Sometimes I also sprinkle a little bit of grated parmesan cheese on top.