In a medium bowl, stir together ground beef, sausage, beaten eggs, breadcrumbs, garlic,
Parmesan, salt, Italian seasoning, and pepper until just combined.
Using a 1-inch cookie scoop or a tablespoon, portion out meatballs, rolling gently with your
hands to shape them. Place meatballs on a plate or a parchment-lined baking sheet.
Set a 6-quart Instant Pot to saute; add olive oil.
When oil is hot, add meatballs in batches; cook turning gently, until browned, about 2 minutes per side. Return browned meatballs to plate or baking sheet.
Add beef stock to Instant Pot; stir to loosen browned bits. Press Cancel to reset Instant Pot.
Return meatballs to Instant Pot. Break pasta in half; add pasta and marinara in layers, ending with marinara.
Place top on Instant Pot; twist to seal and lock. Turn Steam Release Valve to “sealing.”
Set Instant Pot to cook at High Pressure for 8 minutes.
After cooking is complete, manually release the pressure by turning the Steam Release Valve to “venting.”
Remove lid from Instant Pot; stir gently to separate pasta.
Set lid on top of Instant Pot (do not lock); let stand 5 minutes to continue cooking.
Sprinkle servings with Parmesan and basil, if desired.