Pour pasta, water, salt, pepper and butter into 6 qt Instant Pot and stir. Place lid on and turn to lock. Make sure pressure valve is closed. Set to Manual Pressure Cook at high pressure for 4 minutes. When 4 minutes is up, open valve and release pressure immediately. *See Note
Hit or leave the warm button on. Pour in both cheeses and cream and stir until well combined and cheeses are melted. Serve
Note: When opening valve some of the foamy water will spew out. You may want to put a damp towel loosely over the valve or make sure you have in an area that can be wiped up.