In a large bowl, combine 2 tablespoons dried onion, ½ teaspoon garlic powder, beef, rice, celery salt, and pepper.
Mix with your hands until the ingredients are evenly distributed throughout the meat.
Use a 1.5 tablespoon (medium) cookie scoop to portion the meatballs.
Roll each meatball into a nice round ball. Set aside.
Stir the tomato sauce, broth, Worcestershire, remaining 2 tablespoons onion and remaining ½ teaspoon garlic powder together in the Instant Pot inner pot.
Bring sauce to a simmer, stirring regularly.
Nestle the meatballs into the sauce, and spoon a little bit of sauce over the meatballs.
Close and lock the lid.
Turn the pressure release valve to SEALING.
Press MANUAL high pressure and adjust the time to 15 minutes.
Let the pressure release naturally for 15 minutes.
Carefully turn the pressure release valve to VENTING to release any remaining pressure.
Serve the meatballs with the sauce.
Garlic powder: You can use minced garlic in place of the garlic powder if you prefer. Substitute 1 clove minced garlic in the meatballs and a clove minced garlic in the sauce (for a total of two cloves minced).
Ground beef: I recommend using 90% lean ground beef. It's lean enough that the sauce doesn't get too greasy, but it has enough fat that the meatballs don't dry out.
Tomato sauce: Tomato sauce is a canned tomato puree.
Broth: I like to use a reduced-sodium broth. However, feel free to use any broth or stock that you like.