Add stock, 1 tablespoon of butter, garlic, and salt to Instant Pot. Stir. Break spaghetti noodles in half and place in the pot. Using a wooden spoon, push noodles into the stock making sure all are covered.
Secure lid on Instant Pot with pressure valve closed. Select PRESSURE COOK, and set the timer for 1 minute. Once the timer goes off, let the steam release naturally for 12 minutes, then quick release the remaining steam.
Carefully remove the lid from the pot. Add in the remaining 2 tablespoons of butter, Parmesan cheese, and pepper. Stir to combine all ingredients. Taste to adjust salt. Sprinkle on fresh parsley and serve.
**If there is additional liquid in the pot once noodles are cooked, set Instant Pot to saute and cook until absorbed.
