In a large bowl, stir together breadcrumbs, cheese, eggs, buttermilk, garlic, salt, and pepper.
Use your hands to stir in the beef and Italian sausage until *just* combined.
Use a large cookie scoop to scoop the meat mixture into 28 scoops, then use your hands to form them into round meatballs. Set aside on a clean work surface.
Add oil to a 6 quart Instant Pot, then hit SAUTE.
Once it reads HOT, add in 9 meatballs and cook until golden brown on both sides, about 2 minutes per side.
Repeat with remaining meatballs.
Hit CANCEL, then drain the Instant Pot.
Pour in beef broth, scraping up any brown bits from the bottom.
Place the trivet into the Instant Pot, then gently stack the meatballs onto the trivet.
Seal and lock the lid - make sure the pressure valve is pointing toward SEALING.
Cook on HIGH pressure for 7 minutes.
Let pressure naturally release for 5-10 minutes before flipping the pressure valve to release any remaining pressure.
Serve with your favorite marinara sauce and pasta!
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