Stir pasta, water, and salt together in inner steel pot of pressure cooker.
Lock pressure cooker lid in place and set steam vent handle to Sealing. Select Pressure Cook (Manual) and cook on High Pressure for 5 minutes.
Place a dishtowel securely over the steam vent handle to catch any starchy spray that might escape from the vent. Turn steam vent handle to Venting to quick-release pressure. Drain off all but a couple tablespoons of water.
Turn pressure cooker onto Sauté mode – Low.
Stir Cheddar cheese, milk, and butter into pasta until cheese is completely melted. Ladle into bowls and serve immediately.
