Select Sauté and add the bacon to the pressure cooking pot. Cook, stirring frequently, for about 5 minutes, until crisp. Transfer to a paper-towel lined plate, leaving the bacon fat in the pot.
Add the pasta, water, salt, mustard, and cayenne to the pressure cooking pot. Lock the lid in place, select High Pressure and 5 minutes cook time.
When the cook time ends, turn off the pressure cooker and use a quick pressure release. When the valve drops, carefully remove the lid.
Stir in the evaporated milk. (It will look like too much liquid, but it will thicken as it simmers.) Select Sauté on the pressure cooker and simmer until sauce is warm, thickened and pasta is tender, 1 to 3 minutes.
Turn off the pressure cooker. Add both cheeses, a handful at a time, stirring between each addition, until the cheese melts and sauce is smooth. (It’s important to add the cheese a handful at a time so it doesn't clump together.)**
Season with additional salt and pepper to taste.
