Turn your Instant Pot to Saute mode. Melt the Butter inside the pot, then press Cancel to turn off the IP.
Now, add the Pasta, Milk, Heavy Cream, Ground Mustard Powder, Kosher Salt, White Pepper and Cayenne Pepper. Stir Well.
Seal the lid of your pot by turning it until it clicks. Now turn the vent on the top of the lid to the “Sealing” position. Set your pot to High Pressure and use the arrows to set the time for 7 minutes.
The pot will first come to pressure, then countdown 7 minutes, lastly it will notify you it is done. At that point it goes into keep warm mode. It will show the time with an L on the display, counting up the minutes it’s been keeping warm.
Wait until your pot is at L0:05 and then manually release the pressure. To do this, turn the vent from “Sealing” to “Venting”. Steam will immediately flow from the top, so be sure that no part of you is over the pot.
When the pressure indicator drops, turn the pot open and stir in the White Cheddar, Gouda, and Heavy Cream. Let sit for 5 minutes.
Now stir and serve! The pot will continue to keep the food warm if you wish to leave it in the pot for a bit. If it gets a little dry from waiting you can add a splash of milk and stir again.