Add the elbow macaroni and broth to the inner pot.
Close and lock the lid. Make sure that the pressure release valve is set to sealing.
Press manual high pressure and adjust the time to 3 minutes.
When the cooking time has finished, carefully do a controlled pressure release to release the pressure.
Unlock the lid, and give the pasta a good stir.
Add the butter, and stir in until melted.
Alternate adding the cheese and 1 cup of milk, stirring to incorporate. Add additional milk as needed.
Add salt and pepper to taste, and stir in the ground mustard.
Notes
Elbow macaroni: Another shape of pasta will work. Shells and cavatappi are two good options. Other shapes of pasta may require different cooking times.
Chicken broth: I like to use reduced-sodium chicken broth to control the salt. For vegetarian macaroni and cheese, you can use vegetable broth instead of chicken broth.
Butter: I use salted butter.
Cheddar cheese: I like to use sharp or extra sharp cheddar cheese. However, you can use mild or medium cheddar if you prefer.
Milk: The more fat in the milk, the richer the sauce.
Ground mustard: The ground mustard gives the mac and cheese a little bite and flavor.