Step 1

Select SAUTÉ/NORMAL on the Instant Pot. When the pot is hot, add the butter. Once the butter is melted, add the garlic, thyme, and red pepper flakes and cook for about 30 seconds.

Step 2

Add the onion, mushrooms, salt, pepper, and water; stir to combine. Add the fettuccine, pushing it down into the liquid. Add the mascarpone on top of the pasta; do not stir.

Step 3

Secure the lid on the pot. Close the pressure-release valve. Select MANUAL/PRESSURE COOK and set the pot at HIGH pressure for 5 minutes. At the end of the cooking time, allow the pot to sit undisturbed for 5 minutes, then quick-release any remaining pressure.

Step 4

Open the lid and stir. Stir in the Parmesan cheese.

Step 5

Divide the pasta among four dishes, garnish with the thyme, if desired, and serve.