How to Make It
Preheat Instant Pot by setting it to the “saute” function. Spray the insert with cooking spray, and add oil. Add onion, and cook, stirring often, until it begins to soften, 3 minutes. Add beef, salt, garlic, and pepper; cook, stirring often, until browned.
Stir in stock and cream. Press “cancel” on instant pot. Add pasta (do not stir), and up to 1/3 cup of water if pasta isn’t submerged in liquid. Top pasta with marinara (do not stir), and place cover on Instant Pot. Turn steam valve to “sealing” position. Cook on high pressure for 5 minutes (Instant Pot will take about 10 minutes to come to pressure).
When cooking is complete, carefully release the steam valve, and press cancel. When pressure has been released, remove lid, and stir in 1 1/2 cups of the cheese. Top with remaining cheese; let stand 5 to 10 minutes before serving. Sprinkle with fresh basil, if desired.