Add elbow pasta, butter, salt, and water in the Instant Pot. Do not stir the pasta, but gently use a spoon to make sure all pasta is covered with water.
Cook on high pressure for 4 minutes, then quick release carefully.*
Change to "saute mode" and add in cheddar cheese and milk.
Stir to combine until fully melted then remove from heat.
Enjoy immediately!
Video
Notes
* If releasing the pressure causes splatter, stop the release and try again in 10-15 seconds