Set Instant Pot to Saute.
Once the IP is hot melt the butter.
Add the ground beef, let it cook without moving for about 1 minutes, to get a nice sear on it. After that, break it up using a wooden spoon as it cooks.
Once the ground beef has browned, add salt, pepper and Worcestershire sauce. Stir to combine. Add onion, garlic, green pepper and mushrooms. Stir and cook for another 1-2 minutes.
Add the ketchup and beef broth. Stir to combine. Scrape the bottom of the pot with a wooded spoon, to make sure bits are not stuck to it.
Add pasta and stir to combine.
Cover and seal the lid. Make sure the valve points to Sealed. Change setting to manual and adjust time to 5 minutes on High Pressure.
Once Instant Pot beeps to show that it's done, do a quick release, by changing the position of the valve to Vent. Carefully remove cover and stir.
Turn off the Instant Pot.
Top with cheese, put the lid back on but don't seal. Allow a minute or two for cheese to start to melt. Stir to combine.
Serve!
