Turn the Instant Pot to ‘Saute mode.’ Once it displays ‘hot,’ add butter to the insert.
Add macaroni.
Add salt, pepper, and sriracha sauce.
Pour in water /vegetable stock. Please do not add more than 3.5 cups.
Give it a good mix. Close the lid and seal the Instant Pot. Turn 'OFF' the saute mode and pressure cook the macaroni on 'Manual/pressure cook mode' for 5 minutes.
After 5 minutes when the Instant Pot beeps do the QPR ( Quick Release pressure) and turn the Instant Pot 'Off' completely. When the pin drops, carefully open the lid. There will very little stock left at the bottom.
Turn on the Instant Pot in Saute mode - 'Low-pressure setting'. Pour in the cream, milk, and sour cream. Mac and Cheese will be a little soupy at this point. No worries, keep stirring.
Add cheese and give it a good mix. Keep stirring continuously after the cream, sour cream, and cheese are added to the macaroni. Add cheese in batches and mix. Initially, it will look like a clump of cheese. Just hang on and keep stirring until the cheese starts to melt (appx. 2-3 minutes). Soon it will become thick and coat the macaroni well. Turn the Instant Pot OFF.
Add chopped spinach and mix.
Do the taste test and adjust the seasonings. Remove the pot from the base to prevent the mac & cheese from overcooking.
Serve immediately.