When hot, add ground beef and cook, stirring regularly, until cooked through. You want it to keep moving so that it cooks but doesn't brown and stick to the bottom of the inner pot.
Drain the fat and return to inner pot.
Stir in onion.
Cook, stirring regularly, until onion has softened, about 2 minutes.
Add the pasta to the inner pot and pour the chicken broth over the top.
Put the lid on and lock it in place.
Move the pressure release valve to sealing.
Press manual high pressure and adjust the time to 3 minutes.
When the cooking time has finished, turn the pressure release valve to venting.
Stir in the cheese until melted and well-combined.