Add macaroni, water, and salt to the Instant Pot and stir, making sure that all macaroni is submerged in the water.
Secure lid of Instant Pot, making sure valve is turned to “seal.” Set on Manual high pressure for 4 minutes.
When cooking has finished, quick release pressure (see note). When valve lowers, remove cover and stir in evaporated milk, mustard powder, and garlic powder if using. One cup at a time, stir in cheddar and parmesan. Taste and season with pepper as desired.
Serve immediately. (See notes for baking directions.)
This tends to sputter a little when you release the pressure. You can place a towel over the valve to prevent a mess. Just be careful when removing towel because - it will be wet with very hot water.
I prefer to grate my own cheddar cheese. I find it yields a smoother, velvety result. (Plus it’s cheaper!). I have used pre-grated, though, and it also works. It doesn’t stay quite as smooth as it cools, though.
I have made this with whole wheat pasta and it works great!
This also tastes great baked. Bake at 350ºF for 20-30 minutes or until golden brown and a little crispy on the top. Bonus points for a little extra cheese sprinkled on top before you bake it. I have reheated mine this way and it is delicious.