Add pasta, water, House Seasoning Blend, dry mustard and butter to the Instant Pot.
Set Instant Pot to cook on Manual for 6 minutes.
When cooking is finished, quick release the pressure.
There will still be some liquid in the pot - do not drain it.
Stir in the cream cheese and allow it to melt.
Slowly stir in 1/4 cup milk until combined.
Add the cheddar and Monterey Jack cheeses and stir to combine.
Slowly stir in remaining milk until you reach your desired consistency. You may not need all of the remaining milk.