Put the pasta, water, butter, red pepper flakes (optional) and salt in your Instant Pot. (affiliate link)Cook for 5 minutes on the Manual setting.Let the pressure release naturally OR do quick release by putting a clean towel over the pressure release valve and turn the pressure release to manual release. Be careful not to get your hands near the steam. The noodles will have absorbed most of the liquid, but there will be some liquid at the bottom of the pot.Add cheese and milk, stirring gently. If you want a more liquidy Mac and cheese, you can add more milk or cheese until it is the consistency you want.Garnish with sliced green onions.Enjoy!!!